Try building with /W4

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.

Let’s see how clean this is, and impact to devx (mismatched from local warnings) for developers mostly using Clang.

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->