test: Always treat .mir files as tests even outside of CodeGen/MIR

We missed a handful of .mir tests that existed outside the
test/CodeGen/MIR directory.

Also fix the three powerpc .mir tests that nobody noticed were broken.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265350 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed