Supports building gtest as a DLL (by Vlad Losev).

include/gtest/internal/gtest-linked_ptr.h

@@ -77,7 +77,7 @@ namespace testing {
 namespace internal {
 
 // Protects copying of all linked_ptr objects.
-GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex);
+GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex);
 
 // This is used internally by all instances of linked_ptr<>.  It needs to be
 // a non-template class because different types of linked_ptr<> can refer to