Now that we have the Sync class to help construct unit tests that move forward
in a deterministic stepwise order, we can build suitable unit tests for
LLMainThreadTask.

The only usage of any of this was in test code.

Longtime fans will remember that the "dcoroutine" library is a Google Summer
of Code project by Giovanni P. Deretta. He originally called it
"Boost.Coroutine," and we originally added it to our 3p-boost autobuild
package as such. But when the official Boost.Coroutine library came along
(with a very different API), and we still needed the API of the GSoC project,
we renamed the unofficial one "dcoroutine" to allow coexistence.

The "dcoroutine" library had an internal low-level API more or less analogous
to Boost.Context. We later introduced an implementation of that internal API
based on Boost.Context, a step towards eliminating the GSoC code in favor of
official, supported Boost code.

However, recent versions of Boost.Context no longer support the API on which
we built the shim for "dcoroutine." We started down the path of reimplementing
that shim using the current Boost.Context API -- then realized that it's time
to bite the bullet and replace the "dcoroutine" API with the Boost.Fiber API,
which we've been itching to do for literally years now.

Naturally, most of the heavy lifting is in llcoros.{h,cpp} and
lleventcoro.{h,cpp} -- which is good: the LLCoros layer abstracts away most of
the differences between "dcoroutine" and Boost.Fiber.

The one feature Boost.Fiber does not provide is the ability to forcibly
terminate some other fiber. Accordingly, disable LLCoros::kill() and
LLCoprocedureManager::shutdown(). The only known shutdown() call was in
LLCoprocedurePool's destructor.

We also took the opportunity to remove postAndSuspend2() and its associated
machinery: FutureListener2, LLErrorEvent, errorException(), errorLog(),
LLCoroEventPumps. All that dual-LLEventPump stuff was introduced at a time
when the Responder pattern was king, and we assumed we'd want to listen on one
LLEventPump with the success handler and on another with the error handler. We
have never actually used that in practice. Remove associated tests, of course.

There is one other semantic difference that necessitates patching a number of
tests: with "dcoroutine," fulfilling a future IMMEDIATELY resumes the waiting
coroutine. With Boost.Fiber, fulfilling a future merely marks the fiber as
ready to resume next time the scheduler gets around to it. To observe the test
side effects, we've inserted a number of llcoro::suspend() calls -- also in
the main loop.

For a long time we retained a single unit test exercising the raw "dcoroutine"
API. Remove that.

Eliminate llcoro_get_id.{h,cpp}, which provided llcoro::get_id(), which was a
hack to emulate fiber-local variables. Since Boost.Fiber has an actual API for
that, remove the hack.

In fact, use (new alias) LLCoros::local_ptr for LLSingleton's dependency
tracking in place of llcoro::get_id().

In CMake land, replace BOOST_COROUTINE_LIBRARY with BOOST_FIBER_LIBRARY. We
don't actually use the Boost.Coroutine for anything (though there exist
plausible use cases).

If already running on the main thread, LLMaintThreadTask simply runs the work
inline. Otherwise it queues it for the main thread using LLEventTimer, using
std::future to retrieve the result.

The pattern of requiring a lock to permit *any* access to a static instance of
something seems generally useful. Break out lockstatic.h; recast
LLInstanceTracker to use it.

Moving LockStatic to an external template class instead of a nested class in
LLInstanceTrackerBase leaves LLInstanceTrackerBase pretty empty. Get rid of it.

And *that* means we can move the definition of the StaticData used by each
LLInstanceTracker specialization into the class itself, rather than having to
define it beforehand in namespace LLInstanceTrackerStuff.

Define the CMake cache variable, with empty string as its default.

Make build.sh pass the BUGSPLAT_DB environment variable as a CMake
command-line variable assignment.

Change CMake 'if (DEFINED ENV{BUGSPLAT_DB})' to plain 'if (BUGSPLAT_DB)'.

Make CMake pass new --bugsplat switch to every one of SIX different
invocations of viewer_manifest.py.

Give llmanifest.main() function an argument to allow supplementing the base
set of command-line switches with additional application-specific switches.

In viewer_manifest.py, define new --bugsplat command-line switch and pass to
llmanifest.main(). Instead of consulting os.environ['BUGSPLAT_DB'], consult
self.args['bugsplat'].

Pass LL_BUGSPLAT into llapp.cpp compile to be able to detect that.

Use WSTRINGIZE(), LL_TO_WSTRING(), wstringize() to produce required wide
strings. Use a lambda for callback that sends log file; use LLDir, if set, to
find the log file.

Introduce BUGSPLAT CMake variable to allow suppressing BugSplat.
Make BUGSPLAT CMake variable set LL_BUGSPLAT for C++ compilations.

Set viewer version macros on llappviewerwin32.cpp, llappviewerlinux.cpp and
llappdelegate-objc.mm -- because BugSplat needs the viewer version data, and
because the macOS BugSplat hook is engaged in an Objective-C++ function we
override in the app delegate.

No C++ source in llcommon references any of the BugSplat code.

For some reason there wasn't an entry in indra/llcommon/CMakeLists.txt to run
the tests in indra/llcommon/tests/lleventfilter_test.cpp. It seems likely that
at some point it existed, since all previous tests built and ran successfully.
In any case, (re-)add lleventfilter_test.cpp to the set of llcommon tests.
Also alphabetize them to make it easier to find a particular test invocation.

Also add new tests for LLEventThrottle.

To support this, refactor the concrete LLEventThrottle class into
LLEventThrottleBase containing all the tricky logic, with pure virtual
methods for access to LLTimer and LLEventTimeout, and an LLEventThrottle
subclass containing the LLTimer and LLEventTimeout instances and corresponding
implementations of the new pure virtual methods.

That permits us to introduce TestEventThrottle, an alternate subclass with
dummy implementations of the methods related to LLTimer and LLEventTimeout. In
particular, we can explicitly advance simulated realtime to simulate
particular LLTimer and LLEventTimeout behaviors.

Finally, introduce Concat, a test LLEventPump listener class whose function is
to concatenate received string event data into a composite string so we can
readily test for particular sequences of events.

The present CMake logic wants to pass FIXED:NO to the linker for 64-bit
builds, which on the face of it seems like a Good Thing: it permits code to be
relocated in memory, preventing collisions if two libraries happen to want to
load into overlapping address ranges.

However the way it's being specified is wrong and harmful. Passing /FIXED:NO
to the compiler command line engages /FI (Forced Include!) of a nonexistent
file XED:NO -- producing lots of baffling fatal compile errors.

Thanks Callum for diagnosing this!

autobuild 1.1 now supports expanding $variables within a config file --
support that was explicitly added to address this very problem. So now the
windows platform in autobuild.xml uses $AUTOBUILD_ADDRSIZE,
$AUTOBUILD_WIN_VSPLATFORM and $AUTOBUILD_WIN_CMAKE_GEN, which should handle
most of the deltas between the windows platform and windows64.

This permits removing the windows64 platform definition from autobuild.xml.

The one remaining delta between the windows64 and windows platform definitions
was -DLL_64BIT_BUILD=TRUE. But we can handle that instead by checking
ADDRESS_SIZE. Change all existing references to WORD_SIZE to ADDRESS_SIZE
instead, and set ADDRESS_SIZE to $AUTOBUILD_ADDRSIZE. Change the one existing
LL_64BIT_BUILD reference to test (ADDRESS_SIZE EQUAL 64) instead.

We need LLSingleton machinery to be able to reference get_id() without also
depending on all the rest of LLCoros -- since LLCoros isa LLSingleton.

Introduce corresponding llcleanup.cpp, llinitdestroyclass.cpp modules to
contain code that performs logging calls.

Track class::method names for LLInitClass<T> and LLDestroyClass<T> subclasses,
and log them when called. The order in which these calls occur could be
relevant to bugs, and could surface the need to convert to LLSingleton
dependencies.

llexception_test.cpp is an unusual test source in that it need not be verified
on every build, so its invocation in indra/llcommon/CMakeLists.txt is
commented out with that remark. Its purpose is to help a developer decide what
base class(es) to use for LLException, how to throw and how to catch.

Our current conclusions are written up as comments in llexception_test.cpp.

Added CRASH_ON_UNHANDLED_EXCEPTION() and LOG_UNHANDLED_EXCEPTION() macros to
llexception.h -- macros to log __FILE__, __LINE__ and __PRETTY_FUNCTION__ of
the catch site. These invoke functions in llexception.cpp so we don't need to
#include llerror.h for every possible catch site.

This also introduces LLContinueError for exceptions which should interrupt
some part of viewer processing (e.g. the current coroutine) but should attempt
to let the viewer session proceed.

Derive all existing viewer exception classes from LLException rather than from
std::runtime_error or std::logic_error.

Use BOOST_THROW_EXCEPTION() rather than plain 'throw' to enrich the thrown
exception with source file, line number and containing function.

SL-315 WIP - added a call stack extractor for windows to help with tracing joint issues (of course, could be used for other things as well).

because of Oz's suspicion that they may, in some mysterious way, contribute to
code-signing failures.

to a new llcommon/llinitdestroyclass.h.
This mechanism is so general -- but has so many related moving parts -- that
(a) it deserves to be in a header file all its own, instead of conflated with
llui.h, and (b) it should be in llcommon where anyone can use it. It has no
dependencies whatsoever on llui or anything viewer-specific.
In this very changeset we changed one #include "llui.h" whose comment admits
that it was only dragged in for LLDestroyClass.