install: refactor conditional expression

[xtqqczze]

Follow-up to #9526

Contributes to #11274

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail/pipe-f2. tests/tail/pipe-f2 is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Note: The gnu test tests/basenc/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/cut/cut-huge-range is now being skipped but was previously passing.
Congrats! The gnu test tests/pr/bounded-memory is now passing!

[cakebaker]

Thanks!