libexecinfo test: Don't strip installed test

It turns out that a test of backtrace symbol resolution and formatting
requires symbols. Another option mightt be building with -rdynamic instead,
but this works for now.

Re-enabled skipped CI test, as it should now pass.

PR: 241562
Submitted by: lwhsu
Reported by: lwhsu
X-MFC-With: r354126, r354135, r354144