[compiler-rt][CMake] Filter MSVC-specific warning flags from CMAKE_*_FLAGS when building with clang.exe

[gbedwell]

Summary

This fixes a compiler-rt build failure introduced by r231924 (temporarily reverted in r231925 pending this fix).
r231924 modified HandleLLVMOptions.cmake to pass in MSVC warning promotion/suppression flags as flags rather than as definitions ( see http://reviews.llvm.org/D8188 ). This meant that under the (MSVC) condition in CMake, we'd get new flags in the form /wNNNN, /wdNNNN and /weNNNN within CMAKE_*_FLAGS. These are not accepted by clang.exe resulting in an error building compiler-rt within the context of an MSVC build.

I found the existing code that converts from the '/flag' form to the '-flag' form when building with clang.exe under the (MSVC) condition and extended it to remove the above flags entirely.

Thanks,

Greg Bedwell
SN Systems Ltd - Sony Computer Entertainment Group

[kcc]

+rnk

[rnk]

I'm testing an alternative similar to this right now. It'll be easier to write and test it rather than try to get you to write it through code review. :)

[gbedwell]

I'm testing an alternative similar to this right now. It'll be easier to write and test it rather than try to get you to write it through code review. :)

No problem! I shall look forward to it :)

[rnk]

Should be fixed in r232219.

[gbedwell]

Brilliant. I'll give that a go now!

cmake/Modules/CompilerRTCompile.cmake

     string(REPLACE " " ";" global_flags "${CMAKE_C_FLAGS}")
   endif()
   # On Windows, CMAKE_*_FLAGS are built for MSVC but we use the GCC clang.exe
-  # which doesn't support flags starting with "/smth". Replace those with
-  # "-smth" equivalents.
+  # so perform any required transformations to ensure that they are accepted.
   if(MSVC)
+    # The MSVC warning suppression/promotion flags are meaningless and
+    # unsupported here so remove them.
+    string(REGEX REPLACE "/w[de]?[0-9]+(;|$)" "" global_flags "${global_flags}")
+
+    # Replace flags starting with "/smth" with "-smth" equivalents.
     string(REGEX REPLACE "^/" "-" global_flags "${global_flags}")
     string(REPLACE ";/" ";-" global_flags "${global_flags}")
   endif()