libc: Change OK/ERROR macro to enum

to avoid the conflict with 3rd party c++ library(e.g. protobuf):
https://github.com/protocolbuffers/protobuf/blob/fdc35840b95f56c3aef44a3fc6ae5991f21620a5/src/google/protobuf/stubs/status.h#L47

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: Ie8bb9008a8375c729f8b947c9f10baa80104d157

include/sys/types.h

@@ -76,16 +76,6 @@
 #  endif
 #endif
 
-/* POSIX-like OS return values: */
-
-#if !defined(__cplusplus)
-#  undef  ERROR
-#  define ERROR -1
-#endif
-
-#undef  OK
-#define OK 0
-
 /* Scheduling Priorities.
  *
  * NOTES:
@@ -305,6 +295,14 @@ typedef uint64_t u_int64_t;
 
 typedef CODE int (*main_t)(int argc, FAR char *argv[]);
 
+/* POSIX-like OS return values: */
+
+enum
+{
+  ERROR = -1,
+  OK = 0,
+};
+
 #endif /* __ASSEMBLY__ */
 
 /****************************************************************************