Add support for has_feature(cxx_alignof) and has_feature(c_alignof).

r142020 added support for has_feature(cxx_alignas). This does the same for
alignof.

llvm-svn: 223186
diff --git a/clang/test/Lexer/has_feature_cxx0x.cpp b/clang/test/Lexer/has_feature_cxx0x.cpp
index e558f88..9fb05de 100644
--- a/clang/test/Lexer/has_feature_cxx0x.cpp
+++ b/clang/test/Lexer/has_feature_cxx0x.cpp
@@ -234,6 +234,16 @@
 // CHECK-11: has_alignas
 // CHECK-NO-11: no_alignas
 
+#if __has_feature(cxx_alignof)
+int has_alignof();
+#else
+int no_alignof();
+#endif
+
+// CHECK-1Y: has_alignof
+// CHECK-11: has_alignof
+// CHECK-NO-11: no_alignof
+
 #if __has_feature(cxx_raw_string_literals)
 int has_raw_string_literals();
 #else