Do not predefine __EXCEPTIONS in clang-cl (PR19977)

Patch by Ehsan Akhgari! (Test tweak by me.)

Differential Revision: http://reviews.llvm.org/D4065

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210582 91177308-0d34-0410-b5e6-96231b3b80d8