Hoist retrieval of Expr* into caller.  No functionality change.

Just makes the code a little cleaner, and easier to reason about.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173953 91177308-0d34-0410-b5e6-96231b3b80d8
scan-build: When using Xcode 4.6, use build settings for doing proper build interposition.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173954 91177308-0d34-0410-b5e6-96231b3b80d8