This allows adjusting a pattern string so that it matches an entire
string, by wrapping the regex in a group like ^(?:...)$
This is a workaround for the fact that PCRE2_ENDANCHORED is unavailable
on PCRE2 prior to 2017, so we have to adjust the pattern instead.
Also introduce an overload of match() which creates its own
match_data_t.
Let's hope this doesn't causes build failures for e.g. musl: I just
know it's good on macOS and our Linux CI.
It's been a long time.
One fix this brings, is I discovered we #include assert.h or cassert
in a lot of places. If those ever happen to be in a file that doesn't
include common.h, or we are before common.h gets included, we're
unawaringly working with the system 'assert' macro again, which
may get disabled for debug builds or at least has different
behavior on crash. We undef 'assert' and redefine it in common.h.
Those were all eliminated, except in one catch-22 spot for
maybe.h: it can't include common.h. A fix might be to
make a fish_assert.h that *usually* common.h exports.
This migrates our PCRE2 dependency from builtin/string.cpp to new files
re.h/re.cpp, allowing regexes to be used in other places in fish.
No user-visible behavior change expected here.
