Seems that if using PCRE2, we need to escape outer `()` chars and `|`. Sounds
like a bug.
But this is only with some older PCRE2 versions. With >= 10.36, I wasn't able
to reproduce this, everything is fine and working as expected.
Adding _FRR_PCRE2_POSIX definition because pcre2posix.h does not have
include's guard.