One failed self test on Alpine Linux

Hi Everyone,

I'm working on Alpine Linux 3.10, x86_64, fully patched. Alpine is
different because it uses Musl and BusyBox. I'm building Bison from
release tarball 3.7.4. Bison is failing one self test:

    ERROR: 602 tests were run,
    1 failed unexpectedly.
    60 tests were skipped.

It looks like the offender is:

262: R/R cex with prec                               ok
263: Null nonterminals                               FAILED
(counterexample.at:621)
264: Non-unifying Prefix Share                       ok
...

Jeff