[ProfCheck] Add list of xfail tests

This patch contains a list of tests that are currently failing in the
LLVM_ENABLE_PROFCHECK=ON build. This enables passing them to lit through
the LIT_XFAIL env variable. This is necessary for getting a buildbot
spun up to catch regressions while work is being done to fix the
existing issues.

We need to keep this in the LLVM tree so that tests can be removed from
the list at the same time the passes causing issues are fixed.

Author: boomanaiden154