Don't declare and define gmtime()-mutex on Windows platforms

library/platform_util.c

diff --git a/library/platform_util.c b/library/platform_util.c
index ca4d033..ca5fe4f 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -94,7 +94,10 @@
  * threading.h. However, this macro is not part of the Mbed TLS public API, so
  * we keep it private by only defining it in this file
  */
+#if ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) )
 #define PLATFORM_UTIL_USE_GMTIME
+#endif /* ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) ) */
+
 #endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
              ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
                 _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) ) */