openmpi: remove subports for clang 3.3 and 3.4

[mascguy (Christopher Nielsen)]

Presently, openmpi provides subports for the following clang 3.x versions:

• 3.3
• 3.4
• 3.7

That's in addition to clang 5 through 11.

The clang 3.x subports have the following usage statistics, over the past 365 days:

• openmpi-clang33 - zero installs
• openmpi-clang34 - zero installs
• openmpi-clang37 - one install

Of note, sibling MPI port mpich doesn't provide subports for clang 3.x versions; only for 5 through 11.

It's suggested that we remove the subports for clang 3.3 and 3.4, given the usage stats.

[mascguy (Christopher Nielsen)]

As a quick follow-up: While we should continue supporting a wide range of compiler versions, the sheer number of combinations we provide is almost overwhelming.

If we can remove a few of the oldest compilers, that would help a bit with maintaining this port.

[jmroot (Joshua Root)]

Removing these subports may well be the right move, but I wouldn't use the stats to justify it given the small sample size and the "long tail" nature of the data.

[mascguy (Christopher Nielsen)]

Work related to pruning the target compiler list for both openmpi and mpich is being tracked by issue:62807. Closing as duplicate.