[Chapel Merge] Don't try to default-load the PrgEnv-gnu module on

Branch: refs/heads/master
Revision: 1277c26
Author: gbtitus
Log Message:

Merge pull request #16568 from gbtitus/update-tcl-modulefile-again

Don’t try to default-load the PrgEnv-gnu module on EX systems.

(Reviewed by @ronawho.)

The PrgEnv meta-modules do not exist on EX v1.3 and later. So instead
of default-loading PrgEnv-gnu on EX, simply insist that the user have
some cpe module loaded. (The cpe modules are what set PE_ENV in that
environment.) It’s not practical to load one ourselves because the cpe
modules are not meta-modules like the PrgEnv ones, and we’d have to load
all the individual things that go with it.

Modified Files:
M util/build_configs/cray-internal/generate-modulefile.bash

Compare: https://github.com/chapel-lang/chapel/compare/5a3d7ab3166f...1277c26fa692