* Fix std::shared_mutex not found when compiling with clang-cl. LLVM's
RWMutex assumes _MSC_VER is defined only when using the msvc compiler,
but clang-cl also defines it, which uses libc++ that does not define
std::shared_mutex for pre-C++17. To fix it, we also make sure __clang__
is not defined (_MSC_VER and __clang__ implies clang-cl). I will make a
similar upstream fix.

* Fix missing ___chkstk symbol linker error

* Fix "warning C4018: '>': signed/unsigned mismatch" by disabling the
warning.

Bug: b/152339534
Bug: b/161554059
Bug: chromium:1106623
Bug: angleproject:4851
Change-Id: I8639417e3ff78d82477b5ff9699f63507ec2a4ec
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/46628Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>