Make IgnoreParens() look through ChooseExprs.

This is the same way GenericSelectionExpr works, and it's generally a
more consistent approach.

A large part of this patch is devoted to caching the value of the condition
of a ChooseExpr; it's needed to avoid threading an ASTContext into
IgnoreParens().

Fixes <rdar://problem/14438917>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186738 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 4a6f90a..431ee3c 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -610,7 +610,7 @@
   }
 
   llvm::Constant *VisitChooseExpr(ChooseExpr *CE) {
-    return Visit(CE->getChosenSubExpr(CGM.getContext()));
+    return Visit(CE->getChosenSubExpr());
   }
 
   llvm::Constant *VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {