Thanks NickyD.

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).

Also, on Windows, put build output into
build-vc$AUTOBUILD_VSVER-$AUTOBUILD_ADDRSIZE instead of hard-coding
build-vc120-$AUTOBUILD_ADDRSIZE.

Moderately often I want to copy the (long) integration test program path from
build output and rerun the test program by hand. But typically we need
environment variables set as well so it can find its dynamic libraries. This
has resulted in my copying parts of several lines of build output, then
pasting to a command prompt, then hand-tweaking the pasted text so it makes
sense as a command.

Streamline run_build_test.py output so less hand-tweaking is needed.

We expect the viewer-manager package to be self-contained: we expect it to
bring with it any Python packages it requires. We no longer force developers
to wrap third-party Python packages as autobuild packages.

for Windows

instead of relying on both indra/newview/CMakeLists.txt and build.sh
generating the same file pathname.

Make build.sh set VIEWER_SYMBOL_FILE (instead of symbolfile) in pre_build, and
pass it to autobuild configure via -D switch. Then the uploads stanza can just
use VIEWER_SYMBOL_FILE instead of performing its platform-sensitive case
statement right there.

Introduce VIEWER_SYMBOL_FILE CMake cache variable, default empty string.

Make indra/newview/CMakeLists.txt generate_breakpad_symbols logic conditional
on VIEWER_SYMBOL_FILE being non-empty, as well as everything else. Eliminate
local set(VIEWER_SYMBOL_FILE) directives.

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'].

Produce CMake message when BugSplat is engaged so we can detect in build log.

Don't try to copy BugSplat DLLs when NOT engaged.

On TeamCity, set BUGSPLAT_DB from build-secrets.

Use the presence of $BUGSPLAT_DB, rather than a new CMake BUGSPLAT option, to
control whether CMake searches for BugSplat -- and passes LL_BUGSPLAT into C++.

When BUGSPLAT_DB is present, make viewer_manifest.py set "BugSplat DB" in
build_data.json, and "BugsplatServerURL" in Mac Info.plist.

Make llappviewerwin32.cpp read "BugSplat DB" from build_data.json.

Add placeholders for Mac hooks to suppress BugSplat prompt and send
SecondLife.log.

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.

Missed a place in the Copy3rdPartyLibs.cmake file (thank Windows Find) that needs to differentiate between 32 and 64 bit Windows builds