As mentioned in #15, /.configure has to be run with --with-included-regex, as it segfaults without it.

Quoting @rrthomas from the same issue:

It looks like the test for a working re_compile_pattern is segfaulting—that should be fixed. Given that there's already specific Haiku support in this test, it sounds like a bug in the test, or an unexpected bug in Haiku; see regex.m4 for the C source code of the test.