Use -### instead of -ccc-echo.

This is still a fairly odd test. Clang wants to run gcc for assembling. At
least with -### it only prints that instead of actually trying to run it with
-ccc-echo.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186945 91177308-0d34-0410-b5e6-96231b3b80d8