to avoid TeamCity build failures due to 32-bit compiler running out of virtual
memory for precompiled headers.

and the 8.1 SDK) DirectX is included in the SDK and does not need any
special detection logic.

First, get rid of ancient cruft in the find_path() calls: on a 64-bit system,
"$ENV{PROGRAMFILES}" expands to the 64-bit 'Program Files' directory rather
than the 32-bit 'Program Files (x86)' directory, and none of the ancient cruft
would be found there anyway.

Empirically, find_path(dxdiag.h) is able to find the file using environment
variables (INCLUDE from VS variables?), so it doesn't need the specific
pathnames coded into that call.

Once we find DIRECTX_INCLUDE_DIR, don't immediately insert it into
include_directories: we've had troubles with incompatible Windows SDK versions
(compile errors in Microsoft header files!) when DIRECTX_INCLUDE_DIR preceded
the Windows SDK directory in the include path.

The DIRECTX_FIND_QUIETLY logic seemed backwards: the message(STATUS) output was
emitted only when DIRECTX_FIND_QUIETLY was false. Reverse that.

The ancient cruft in find_path(dxguid.lib) was causing it to find the wrong
(very old) DirectX library. Remove ancient cruft. But empirically, without
that, even once we've found DIRECTX_INCLUDE_DIR, CMake could not implicitly
find dxguid.lib. If the DirectX directory hierarchy were structured as
.../version/Include and .../version/Lib, a relative pathname would have been
sufficient hint. Unfortunately it's structured as .../Include/version and
.../Lib/version, so a relative pathname would have to include the specific
version. Instead, replace "/Include/" with "/Lib/". But even then, we have to
drill down to the architecture-specific subdirectory based on ADDRESS_SIZE.

Specify all of msvcp$VER.dll, msvcr$VER.dll and vcruntime$VER.dll -- but check
each of them individually, because any given VS release has only a subset of
those. Add messaging to clarify what we're doing.

Introduce to_staging_dirs CMake macro to cut down on redundant boilerplate:
the idiom in which we use copy_if_different twice, once to the Release staging
directory and once to the RelWithDebInfo staging directory, each time
appending the target pathnames to third_party_targets. Replace that idiom with
calls to to_staging_dirs.

Evidently, with VS 2017, what would have been msvcr140.dll has become
vcruntime140.dll instead. msvcr140.dll is no longer a good sample DLL for
which to search.

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.