Move generic MIR tests in their own subdir, requires "native" as well

These tests rely on the native backend to be built-in.

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243959 91177308-0d34-0410-b5e6-96231b3b80d8
21 files changed