Fix to declare missing `snprintf` prototype at correct place

Signed-off-by: OBATA Akio <obache@wizdas.com>
(cherry picked from commit f65c9e6665)

config.h.cmake

@@ -1134,7 +1134,7 @@ __END_DECLS
 
 
 
-#if !defined(HAVE_VSNPRINTF_PROTO)
+#if !defined(HAVE_VSNPRINTF_PROTO) || !defined(HAVE_SNPRINTF_PROTO)
 #if __STDC__
 #include <stdarg.h>
 #include <stdlib.h>
@@ -1144,11 +1144,15 @@ __END_DECLS
 #ifdef __cplusplus
 extern "C"
 #endif
+#if !defined(HAVE_VSNPRINTF_PROTO)
 int vsnprintf(char *str, size_t n, char const *fmt, va_list ap);
+#endif
+#if !defined(HAVE_SNPRINTF_PROTO)
+int snprintf(char *str, size_t n, char const *fmt, ...);
+#endif
 #ifdef __cplusplus
 extern "C"
 #endif
-int snprintf(char *str, size_t n, char const *fmt, ...);
 #endif