Split TestGlobalVariables into two and xfail one of them for arm64 linux

Split TestGlobalVariables into two and xfail one of them for arm64 linux

Displaying of global pointer variables is not working on arm64 linux
(pr37301).

I've moved this part into a separate test, so it can be xfailed
separately. I then move the "show-variables-with-process-available"
check before the "show-all-variables" command to presrve the intent of
checking that global variable caching works correctly. (I've verified
that the new arrangement still fails when I revert the fix from
r331230.)

llvm-svn: 331250