libc: tag missing functions in system headers.
This matches recent changes in the NDK header.
We enclose missing functions in #if 0 .. #endif blocks
with a clear "MISSING" in comments in order to locate
them later.
Change-Id: I87b3a62e777897e75c9243360fb0a82bcc53d9fb
diff --git a/libc/include/sched.h b/libc/include/sched.h
index 33b9ad6..e702470 100644
--- a/libc/include/sched.h
+++ b/libc/include/sched.h
@@ -69,7 +69,7 @@
#define CLONE_CHILD_SETTID 0x01000000
#define CLONE_STOPPED 0x02000000
-#ifdef __GNU_SOURCE
+#ifdef _GNU_SOURCE
extern int clone(int (*fn)(void *), void *child_stack, int flags, void* arg, ...);
#endif