Add C11 <stdatomic.h>.
Bug: 14903517
Change-Id: I631dbfdaa698cf7fea8e3b5e18a32586383e62a5
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 685de32..0286616 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -38,6 +38,24 @@
#define _SYS_CDEFS_H_
/*
+ * Testing against Clang-specific extensions.
+ */
+
+#ifndef __has_extension
+#define __has_extension __has_feature
+#endif
+#ifndef __has_feature
+#define __has_feature(x) 0
+#endif
+#ifndef __has_include
+#define __has_include(x) 0
+#endif
+#ifndef __has_builtin
+#define __has_builtin(x) 0
+#endif
+
+
+/*
* Macro to test if we're using a GNU C compiler of a specific vintage
* or later, for e.g. features that appeared in a particular version
* of GNU C. Usage: