Robustify the @encode code and add support for _Atomic.

Fixes PR14628.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170639 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/CodeGenObjC/encode-test.m b/test/CodeGenObjC/encode-test.m
index 3780068..e8d6541 100644
--- a/test/CodeGenObjC/encode-test.m
+++ b/test/CodeGenObjC/encode-test.m
@@ -165,3 +165,7 @@
 // rdar://9622422
 // CHECK: @g11 = constant [2 x i8] c"v\00"
 const char g11[] = @encode(void);
+
+// PR14628
+// CHECK: @g12 = constant [3 x i8] c"Ai\00"
+const char g12[] = @encode(_Atomic(int));