This patch adds a large number of missing includes in the libc++ headers
and the test suite. Those were found as part of the effort to move
towards a mostly monolithic top-level std module.
This is the last PR that's needed (for now) to get libc++'s tests
working with MSVC's STL.
The ADDITIONAL_COMPILE_FLAGS machinery is very useful, but also very
problematic for MSVC, as it doesn't understand most of Clang's compiler
options. We've been dealing with this by simply marking anything that
uses ADDITIONAL_COMPILE_FLAGS as FAIL or SKIPPED, but that creates
significant gaps in test coverage.
Fortunately, ADDITIONAL_COMPILE_FLAGS also supports "features", which
can be slightly enhanced to send Clang-compatible and MSVC-compatible
options to the right compilers.
This patch adds the gcc-style-warnings and cl-style-warnings Lit features,
and uses that to pass the appropriate warning flags to tests. It also uses
TEST_MEOW_DIAGNOSTIC_IGNORED for a few local suppressions of MSVC
warnings.
This patch introduces the support::make_test_jthread utility which is
basically the same as support::make_test_thread but for std::jthread. It
allows vendors to maintain a downstream way to create threads for use
within the test suite, which is especially useful for embedded
platforms.
