This is in preparation for porting `GRegex` to libpcre2, which is
happening in !2529. It’s a big port, though, and specially rebuilding
the CI images to add libpcre2 for it is a pain.
Add libpcre2, and then !2529 can drop the old libpcre dependencies when
the port lands.
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #1085
