Raise PGI version floor to 19.3

[Dan Bonachea]

As described in this thread on PR 397, bugs in the PGI optimizer observed on all platforms through compiler version 19.1 prevent it from correctly optimizing the upcxx::copy() implementation, which was overhauled in that PR.

After some non-trivial investment of effort, we were unsuccessful in finding an acceptable workaround that would ensure this buggy optimizer continued to correctly compile upcxx::copy().

As agreed, I'll be raising our supported PGI version floor to 19.3 to ensure that end users don't encounter this problem.

[Dan Bonachea]

Implemented in PR 401

[Dan Bonachea]

issue #527: Raise PGI version floor to 19.3

Resolves issue #527

→ <<cset 691c228a322d>>