Revert "[ci/arm/darwin/testsuite] Forwards ports from GHC-8.10"

This commit squashed away useful history and should have been merged as individual commits. Moreover, one of the original commits breaks binary distribution installation on Darwin (#19640). Reverting wholesale so we can re-merge as individual commits.

This reverts commit 0cbdba27.

@angerman, I have a few things that I would like to see fixed in the next iteration of this, some of which I've noted in the past:

• Certainly don't squash away the history given that there are functional changes in this branch
• The timing logic should live in ci.sh, not duplicated in gitlab-ci.yml.
• [darwin] stop the DYLD_LIBRARY_PATH madness regresses binary distribution install; dropping prependLibraryPath is not in general safe on Darwin since we rely on make install.
• It is quite surprising that CONFIGURE_ARGS is overridden by shell.nix; let's not do this. Let's rather just append to it CONFIGURE_ARGS.
• We should not be ignoring LLVM version mismatches from the testsuite. Again, either we should widen the accepted version range or change the compiler version used in CI.

If you don't have time to handle this, I would be happy to take care of these issues. In the meantime, I'm going to revert.