Provide, and document, a set of __c11_atomic_* intrinsics to implement C11's
<stdatomic.h> header.

In passing, fix LanguageExtensions to note that C11 and C++11 are no longer
"upcoming standards" but are now actually standardized.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@154513 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/CodeGen/atomic_init.c b/test/CodeGen/atomic_init.c
index 243eb60..6f773be 100644
--- a/test/CodeGen/atomic_init.c
+++ b/test/CodeGen/atomic_init.c
@@ -9,6 +9,6 @@
 {
   _Atomic(int) j = 12; // CHECK: store 
                        // CHECK-NOT: atomic
-  __atomic_init(&j, 42); // CHECK: store 
-                         // CHECK-NOT: atomic
+  __c11_atomic_init(&j, 42); // CHECK: store 
+                             // CHECK-NOT: atomic
 }