When LLVM is not built with zlib, nocompression.s will test
for the error message. But this test case will cause breakage
because the exit code is non-zero. This commit fix this issue
by adding "not" to the command.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205102 91177308-0d34-0410-b5e6-96231b3b80d8