Add some glibc-like #defines for libchrome.

libchrome uses __USE_XOPEN2K8 to decide whether futimens is
available. That's perhaps not the best idea, but there are other
cases where we defined the same feature macros as glibc to aid
portability.

(cherry picked from commit 7ea817d39ecfdb0f42a61ea87c81105461710a93)

Change-Id: I003442825778b5b2bcbbd4938eb213e581c355ed
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 04613f4..7df8b60 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -520,6 +520,11 @@
 #include <android/api-level.h>
 
 /* glibc compatibility. */
+#if __POSIX_VISIBLE >= 200809
+#define __USE_ISOC99 1
+#define __USE_XOPEN2K 1
+#define __USE_XOPEN2K8 1
+#endif
 #if __LP64__
 #define __WORDSIZE 64
 #else