Revert "Disable all llvm-config tests for now, will investigate later"

This reverts commit r260386.

These tests all pass for me locally. I have no idea if they will pass on all configurations, so I'll watch the bots closely.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289490 91177308-0d34-0410-b5e6-96231b3b80d8