Rationalize visibility.

If it's C or POSIX, it's in. If it's BSD or GNU, it's guarded by __USE_BSD
or __USE_GNU.

Bug: https://code.google.com/p/android/issues/detail?id=194631
Change-Id: Ife51a21c2b37b060db56780d29c929805b199cb6
diff --git a/libc/include/sys/stat.h b/libc/include/sys/stat.h
index f26a492..0a999e4 100644
--- a/libc/include/sys/stat.h
+++ b/libc/include/sys/stat.h
@@ -128,7 +128,7 @@
 #define st_mtimensec st_mtim.tv_nsec
 #define st_ctimensec st_ctim.tv_nsec
 
-#ifdef __USE_BSD
+#if defined(__USE_BSD)
 /* Permission macros provided by glibc for compatibility with BSDs. */
 #define ACCESSPERMS (S_IRWXU | S_IRWXG | S_IRWXO) /* 0777 */
 #define ALLPERMS    (S_ISUID | S_ISGID | S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO) /* 07777 */