Do not cache a pointer to ExprEvalContexts.back().

It may become a dangling pointer if the underlying SmallVector reallocates.
Sadly the testcase is really large and doesn't reduce well because of
SmallVector's reallocation patterns.

Fixes PR14336.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168045 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed