Exclude win32 from hidden visibility checks.

Tests/Module/CheckCXXCompilerFlag/CMakeLists.txt

@@ -41,7 +41,9 @@ check_cxx_compiler_flag(-fvisibility=hidden HAS_HIDDEN_VISIBILITY)
 message("HAS_HIDDEN_VISIBILITY: ${HAS_HIDDEN_VISIBILITY}\n\nCOMPILE OUTPUT:\n${OUTPUT}")
 
 if(CMAKE_COMPILER_IS_GNUCXX)
-  test_pass(HAS_HIDDEN_VISIBILITY "GCC should support hidden visibility, but does not.")
+  if(NOT WIN32)
+    test_pass(HAS_HIDDEN_VISIBILITY "GCC should support hidden visibility, but does not.")
+  endif()
 else()
   message("Unhandled Platform")
 endif()