Check whether _MSC_VER is defined when detecting presence of cxxabi.h under libc++.

If _MSC_VER is defined, it means that we are using the Microsoft
ABI, so cxxabi.h (which is associated with the Itanium ABI) will not
be available.

googletest/include/gtest/internal/gtest-port.h

@@ -980,7 +980,7 @@ using ::std::tuple_size;
 #endif
 
 // _LIBCPP_VERSION is defined by the libc++ library from the LLVM project.
-#if defined(__GLIBCXX__) || defined(_LIBCPP_VERSION)
+#if defined(__GLIBCXX__) || (defined(_LIBCPP_VERSION) && !defined(_MSC_VER))
 # define GTEST_HAS_CXXABI_H_ 1
 #else
 # define GTEST_HAS_CXXABI_H_ 0