fix wrong target detection

For mingw with `-std=c99`, WIN32 is not defined.

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/tests/suites/test_suite_platform.function b/tests/suites/test_suite_platform.function
index 6ae1026..61681b8 100644
--- a/tests/suites/test_suite_platform.function
+++ b/tests/suites/test_suite_platform.function
@@ -10,7 +10,8 @@
 #if defined(MBEDTLS_HAVE_TIME)
 #include "mbedtls/platform_time.h"
 
-#ifdef WIN32
+#if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || \
+    defined(__MINGW32__) || defined(_WIN64)
 #include <windows.h>
 #elif _POSIX_C_SOURCE >= 199309L
 #include <time.h>
@@ -19,7 +20,8 @@
 #endif
 void sleep_ms(int milliseconds)
 {
-#ifdef WIN32
+#if defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || \
+    defined(__MINGW32__) || defined(_WIN64)
     Sleep(milliseconds);
 #elif _POSIX_C_SOURCE >= 199309L
     struct timespec ts;