avoid setting FILE lock count when not using flockfile

for now this is just a tiny optimization, but later if we support
cancellation from __stdio_read and __stdio_write, it will be necessary
for the recusrive lock count to be zero in order for these functions
to know they are responsible for unlocking the FILE on cancellation.

src/stdio/__lockfile.c

@@ -8,7 +8,7 @@ int __lockfile(FILE *f)
 		return 0;
 	while ((owner = a_cas(&f->lock, 0, tid)))
 		__wait(&f->lock, &f->waiters, owner, 1);
-	return f->lockcount = 1;
+	return 1;
 }
 
 void __unlockfile(FILE *f)