[compiler-rt] [test] [fuzzer] Don't pass msvc specific flags to mingw tools

[mstorsjo]

Summary

This fixes building the tests so that the tests can start
executing (even if there still are lots of failures).

[vitalybuka]

What is about clang-cl?

[mstorsjo]

In D147648#4246717, @vitalybuka wrote:

What is about clang-cl?

When building with clang-cl, the cmake variable MSVC is set, since it’s considered roughly the same. (It’s considered the same “environment “.) Distinguishing between clang-cl and actual MSVC requires checking more specific variables.

[vitalybuka]

In D147648#4246736, @mstorsjo wrote:

In D147648#4246717, @vitalybuka wrote:

What is about clang-cl?

When building with clang-cl, the cmake variable MSVC is set, since it’s considered roughly the same. (It’s considered the same “environment “.) Distinguishing between clang-cl and actual MSVC requires checking more specific variables.

Thanks, we are good if it's covered.

[phosek]

LGTM

compiler-rt/lib/fuzzer/tests/CMakeLists.txt

 set_target_properties(FuzzerUnitTests PROPERTIES FOLDER "Compiler-RT Tests")
 
 add_custom_target(FuzzedDataProviderUnitTests)
 set_target_properties(FuzzedDataProviderUnitTests PROPERTIES FOLDER "Compiler-RT Tests")
 
 set(LIBFUZZER_UNITTEST_LINK_FLAGS ${COMPILER_RT_UNITTEST_LINK_FLAGS})
 list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS --driver-mode=g++)
 
-if(WIN32)
+if(MSVC)
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -Wl,-defaultlib:libcmt,-defaultlib:oldnames)
 else()
   if (APPLE)
     list(APPEND LIBFUZZER_UNITTEST_CFLAGS -isysroot ${DARWIN_osx_SYSROOT})
     list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -isysroot ${DARWIN_osx_SYSROOT})
   endif()
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lpthread)
 endif()