To avoid having "#if HAVE_PCRE2" all throughout the code, let's
confine the pcre2 header specific stuff to pcre2-util.c. Instead of
exposing all the individual symbols from pcre2, let's only expose
three high level functions that do all we need:
- pcre2_pattern_compile(): Compile the regex
- pcre2_pattern_matches(): Check if the compiled regex matches a message
- pcre2_pattern_free(): Free the compiled regex
We expose the compiled pcre2 pattern (which is of type pcre2_code *) as
a void pointer to avoid having to include pcre2.h in all code where we
work with compiled pcre2 patterns. For readability, we typedef void
to pcre2_pattern and use that as the type specifier for compiled pcre2
patterns.
We already store the dlopen() stuff for other libraries in util headers
as well so let's do the same for pcre2. We also move the definition of
some trivial cleanup functions from journalctl.c to pcre2-util.h
Daan De Meyer