-fms-extensions: Don't define __PRETTY_FUNCTION__ to __FUNCTION__

This reverts r90596 from 2009. Having this macro definition makes Clang
strictly less useful with -fms-extensions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205729 91177308-0d34-0410-b5e6-96231b3b80d8
Thread Safety Analysis: fix warning.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@205733 91177308-0d34-0410-b5e6-96231b3b80d8