Implement parsing and semantic checking of the 'mutable' keyword.
Thanks to Doug for the review. Actual effects of mutable to follow.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59331 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Parser/cxx-class.cpp b/test/Parser/cxx-class.cpp
index ef0c901..5afa8d6 100644
--- a/test/Parser/cxx-class.cpp
+++ b/test/Parser/cxx-class.cpp
@@ -21,6 +21,7 @@
   int x,f(),y,g();
   inline int h();
   static const int sci = 10;
+  mutable int mi;
 };
 void glo()
 {