Make expression allocation methods use a 'const' reference to the ASTContext since the underlying operator new only needs a const reference.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188636 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Stmt.cpp b/lib/AST/Stmt.cpp
index 6a39996..87e55a2 100644
--- a/lib/AST/Stmt.cpp
+++ b/lib/AST/Stmt.cpp
@@ -49,12 +49,12 @@
   return StmtClassInfo[E];
 }
 
-void *Stmt::operator new(size_t bytes, ASTContext& C,
+void *Stmt::operator new(size_t bytes, const ASTContext& C,
                          unsigned alignment) throw() {
   return ::operator new(bytes, C, alignment);
 }
 
-void *Stmt::operator new(size_t bytes, ASTContext* C,
+void *Stmt::operator new(size_t bytes, const ASTContext* C,
                          unsigned alignment) throw() {
   return ::operator new(bytes, *C, alignment);
 }