Build with MSVC /W4 (#1432)

Summary:
X-link: https://github.com/facebook/react-native/pull/41044

The reference Clang/GCC build has a pretty strict set of warnings enabled. The reference MSVC build has less strict warnings, which can be a problem for MSVC users building at higher warning levels (e.g. React Native for Windows in OSS uses `/W4` as its baseline warning level).

This bumps up the MSVC warning level to `/W4`, since we are nearly clean already.

There are some limitations. E.g. we don't test binary with MSVC (some issues I didn't work out), and only test building statically linked. But but we do have a minimal C benchmark we compile with MSVC.

Pull Request resolved: https://github.com/facebook/yoga/pull/1432

Test Plan: GitHub Actions running benchmark MSVC build.

Reviewed By: yungsters

Differential Revision: D50398443

Pulled By: NickGerleman

fbshipit-source-id: 6616034d79b1a308b32d5d3387bae70f40b7b5ab

cmake/project-defaults.cmake

@@ -17,7 +17,7 @@ add_compile_options(
     # "Standard C++ exception handling" (C++ stack unwinding including extern c)
     /EHsc
     # Enable warnings and warnings as errors
-    /W3
+    /W4
     /WX
     # Disable RTTI
     $<$<COMPILE_LANGUAGE:CXX>:/GR->