Avoid warning on "clang -c -Dfoo test.i". Lines like these are created
when using ccache and libtool.m4 assumes that the compiler cannot print
warnings about options it knows about.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@135723 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed