[Chapel Merge] Update libunwind docs and improve error messages

Branch: refs/heads/main
Revision: 8226206e44d7c02f23f81ebc013ce91ba4d003a8
Author: jabraham17
Link: Update libunwind docs and improve error messages by jabraham17 · Pull Request #28147 · chapel-lang/chapel · GitHub
Log Message:
Update libunwind docs and improve error messages (#28147)

Updates the libunwind docs to reflect the new defaults changed in this
release

Additionally, this PR improves the error that users could get it they
explicitly set CHPL_LIBUNWIND and libunwind is not available.

[reviewed by @dlongnecke-cray]

Compare: Comparing e8def2539c17f1d9ca15a196aa513acea6cad83e...79e0a34f90055bcc34dddcf3ba0beb16bffd8559 · chapel-lang/chapel · GitHub

Diff:
M doc/rst/usingchapel/chplenv.rst
M util/chplenv/chpl_unwind.py
https://github.com/chapel-lang/chapel/pull/28147.diff