[-Wunreachable-code] Teach reachable code analysis heuristics about more literal types.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203193 91177308-0d34-0410-b5e6-96231b3b80d8
[-Wunreachable-code] Correctly expand artificial reachability to pruned '&&' and '||' branches involving configuration values.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203194 91177308-0d34-0410-b5e6-96231b3b80d8