Avoid definining more GCC specific predefined macros in clang-cl

Reviewers: hansw, rnk

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4419

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212753 91177308-0d34-0410-b5e6-96231b3b80d8