Fix some -Wabsolute-value warnings introduced in r207796.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207806 91177308-0d34-0410-b5e6-96231b3b80d8
do not hide clang stderr output during a test

I don't know why this fails on the buildbot.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207808 91177308-0d34-0410-b5e6-96231b3b80d8
Use %clang_cc1 in rewrite-includes-messages.c test and drop REQUIRES: shell

This test passes on Windows with lit's shell interpreter.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@207810 91177308-0d34-0410-b5e6-96231b3b80d8