sys/types.h: Fixed the conflict issue with the "OK" constant definition

When cross-compiling PSE52 VSX testcases based on Vela, VSX defines its
own "OK" constant as a macro, which conflicts with the "OK" constant
defined as an enum in <sys/types.h>. To ensure compatibility, we
have undef'd the macro version of "OK" in advance.

Signed-off-by: guoshichao <guoshichao@xiaomi.com>

include/sys/types.h

@@ -317,6 +317,10 @@ typedef CODE int (*main_t)(int argc, FAR char *argv[]);
 
 /* POSIX-like OS return values: */
 
+#ifdef OK
+#  undef OK
+#endif
+
 enum
 {
   ERROR = -1,