move stdio locking MAYBE_WAITERS definition to stdio_impl.h

don't repeat definition in two places.

src/internal/stdio_impl.h

@@ -94,6 +94,8 @@ hidden void __register_locked_file(FILE *, struct __pthread *);
 hidden void __unlist_locked_file(FILE *);
 hidden void __do_orphaned_stdio_locks(void);
 
+#define MAYBE_WAITERS 0x40000000
+
 hidden void __getopt_msg(const char *, const char *, const char *, size_t);
 
 #define feof(f) ((f)->flags & F_EOF)

src/stdio/__lockfile.c

 #include "stdio_impl.h"
 #include "pthread_impl.h"
 
-#define MAYBE_WAITERS 0x40000000
-
 int __lockfile(FILE *f)
 {
 	int owner = f->lock, tid = __pthread_self()->tid;

src/stdio/ftrylockfile.c

@@ -2,8 +2,6 @@
 #include "pthread_impl.h"
 #include <limits.h>
 
-#define MAYBE_WAITERS 0x40000000
-
 void __do_orphaned_stdio_locks()
 {
 	FILE *f;