Fixed compilation on mingw with secure APIs enabled by default.

If MINGW_HAS_SECURE_API is defined, we don't need to declare strtok_s, but we still need strtok_r define.

Change-Id: I7cf781bb58f991a2bdce6a2ccf5082f6924579a3
diff --git a/vpx/src/svc_encodeframe.c b/vpx/src/svc_encodeframe.c
index 4f5ba6f..adce476 100644
--- a/vpx/src/svc_encodeframe.c
+++ b/vpx/src/svc_encodeframe.c
@@ -23,11 +23,13 @@
 #include "vpx/vp8cx.h"
 #include "vpx/vpx_encoder.h"
 
-#if defined(__MINGW32__) && !defined(MINGW_HAS_SECURE_API)
+#ifdef __MINGW32__
 #define strtok_r strtok_s
+#ifndef MINGW_HAS_SECURE_API
 // proto from /usr/x86_64-w64-mingw32/include/sec_api/string_s.h
 _CRTIMP char *__cdecl strtok_s(char *str, const char *delim, char **context);
-#endif
+#endif  /* MINGW_HAS_SECURE_API */
+#endif  /* __MINGW32__ */
 
 #ifdef _MSC_VER
 #define strdup _strdup