Understand unary operators after "return" and "case".

This fixes llvm.org/PR14746.

Before: return - 1;
After:  return -1;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171389 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed