Update WindowsBuild.md

Now that the flags have been fixed for the runtime build, we no longer need to ignore the overly verbose warnings.  We now emit warnings which we should really cleanup.

Author: compnerd

docs/WindowsBuild.md

@@ -157,7 +157,6 @@ cmake -G Ninja^
  -DCMAKE_BUILD_TYPE=RelWithDebInfo^
  -DCMAKE_C_COMPILER=clang-cl^
  -DCMAKE_CXX_COMPILER=clang-cl^
- -DCMAKE_CXX_FLAGS:STRING="-Wno-c++98-compat -Wno-c++98-compat-pedantic"^
  -DCMAKE_EXE_LINKER_FLAGS:STRING="/INCREMENTAL:NO"^
  -DCMAKE_SHARED_LINKER_FLAGS:STRING="/INCREMENTAL:NO"^
  -DSWIFT_BUILD_SOURCEKIT=ON^