CMake: Set warning options for MSVC so we can enable /WX

Reduce default set from /W3 to /W2 and disable two
additional warnings that we do not care about.

With these settings successful builds with /WX are possible.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>

cmake/findcoredeps.cmake

@@ -123,8 +123,9 @@ function(add_core_dependencies target)
  endif ()
 
  if (MSVC)
- # I think this is too much currently
- # target_compile_options(${target} PRIVATE /W4)
+ # C4200: nonstandard extension used : zero-sized array in struct/union
+ # C4146: unary minus operator applied to unsigned type, result still unsigned
+ target_compile_options(${target} PRIVATE /W2 /wd4200 /wd4146)
  else()
  target_compile_options(${target} PRIVATE -Wall -Wsign-compare)
  if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")