[lld] [lld][llvm-lit] Enabled lit internal shell for lld test suite (PR #106651)

[Paul Kirth via llvm-commits]

ilovepi wrote:

I agree we should avoid loss of coverage when possible. 

One thing that would be good is to get a buildbot configuration in CI that uses the internal shell (aside from Windows), so these test suites don’t regress during the migration period. I wonder if there is a good bot candidate we can use? Preferably one that has substantial overlap with other configurations. Since the internal shell is reportedly faster, maybe the presubmit bots?

Another option would be to give lit a 3rd mode to run in, where it runs  only tests with REQUIRES: shell in the external shell, but all the other tests in the internal shell. 

For now let’s create (or update?) a bug for the migration of the tests and note that this patch is blocked on that work. 

https://github.com/llvm/llvm-project/pull/106651