For all RUN lines starting with "not", redirect stderr to /dev/null so tests

For all RUN lines starting with "not", redirect stderr to /dev/null so tests
don't fail when (expected) error output is produced. This fixes 17 tests.

While I was there, I also made all RUN lines of the form "not llvm-as..." a bit
more consistent, they now all redirect stderr and stdout to /dev/null and use
input redirect to read their input.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52174 91177308-0d34-0410-b5e6-96231b3b80d8