[Chapel Merge] Restore default `-lgmp` on Cray X* systems

Branch: refs/heads/main
Revision: 93ecf28dc88927e3dd619addd3cbbeecbffea286
Author: jabraham17
Link: Restore default `-lgmp` on Cray X* systems by jabraham17 · Pull Request #25216 · chapel-lang/chapel · GitHub
Log Message:
Restore default -lgmp on Cray X* systems (#25216)

On Cray X* systems, gmp should be in the default library search and does
not require pkg-config

Restores the behavior prior to

Tested that this change allows a system gmp to be used on a Cray XC
without pkg-config

Note: We could also do something like $CHPL_TARGET_COMPILER --print-file-name=libgmp.so to check if a shared library is available
in PATH, rather than special casing for platforms. But that has the
potential to cause problems, so this close to a release I just restored
the previous behavior.

[Reviewed by @jhh67]

Compare: Comparing bd65c6dc3993127df1c35ca16033fabe05ee9c1c...43aebb55382bbb4c0b38759f79204700cba52887 · chapel-lang/chapel · GitHub

M third-party/Makefile
M util/chplenv/chpl_gmp.py
M util/chplenv/third_party_utils.py