fa7719a changed syntax for specifying exact versions, which are
required for some compiler specs (including those read as part
of parsing a Cray manifest). This fixes that and also makes a
couple other improvements to manifest parsing.
* Instantiate compiler specs with exact versions (fixes#37893)
* fix slingshot network detection (CPE 22.10+ has libcxi.so
in /usr/lib64)
* "spack external find": add arg to ignore default dir for cray
manifests
0f84782fcc