[Chapel Merge] Fix some OSX-specific test failures

Branch: refs/heads/main
Revision: 4c32b4426771dbccd5b990c200c32ac187cbfbe3
Author: dlongnecke-cray
Link: Fix some OSX-specific test failures by dlongnecke-cray · Pull Request #28666 · chapel-lang/chapel · GitHub
Log Message:
Fix some OSX-specific test failures (#28666)

The regex flags I used aren't supported on OSX, so switch to perl
instead. Add a darwin-specific .prediff for another test I added.

Compare: Comparing 2e916fc3fc7a9f06fea3f4408e428bb667a0c457...91eead087b6a946a096f4f342ffa7db9de310b2c · chapel-lang/chapel · GitHub

Diff:
A test/interop/C/errorMessage/OpaqueCTypeAliasVerify.darwin.good
M test/interop/C/use_OpaqueCharAlias.prediff
https://github.com/chapel-lang/chapel/pull/28666.diff