gtest-all.cc: quiet an unused variable warning

under windows / mingw builds

Change-Id: I93f9a5df77cea0c28d4afb272abcde5a9732e355

third_party/googletest/README.libvpx

@@ -16,4 +16,6 @@ Local Modifications:
   free build.
 - Added GTEST_ATTRIBUTE_UNUSED_ to test registering dummies in TEST_P
   and INSTANTIATE_TEST_CASE_P to remove warnings about unused variables
-  under GCC 5.
+  under GCC 5.
+- Only define g_in_fast_death_test_child for non-Windows builds; quiets an
+  unused variable warning.

third_party/googletest/src/src/gtest-all.cc

@@ -6612,9 +6612,11 @@ GTEST_DEFINE_string_(
 
 namespace internal {
 
+# if !GTEST_OS_WINDOWS
 // Valid only for fast death tests. Indicates the code is running in the
 // child process of a fast style death test.
 static bool g_in_fast_death_test_child = false;
+# endif  // !GTEST_OS_WINDOWS
 
 // Returns a Boolean value indicating whether the caller is currently
 // executing in the context of the death test child process.  Tools such as