Determine/document support for PrgEnv-intel

[Paul Hargrove]

Perlmutter now has PrgEnv-intel, which we explicitly document as untested.

As soon as we have enough nightly regression testing, I need to update the docs and possibly the logic in system-checks.sh (though there are no warnings currently).

[Paul Hargrove]

As noted in issue 603, I've confirmed that version 2023.1.0 of the oneAPI compilers is free of compiler-specific failures on Perlmutter. Weekly automated runs will begin this Saturday.

[Paul Hargrove]

docs: list support for PrgEnv-intel on HPE Cray EX

This commit resolves issue #602 by adding PrgEnv-intel to two lists of supported environments on the HPE Cray EX platform.

→ <<cset 8bf943327fd9>>