drop embedded pcre copy
Submitted by Christian Persch
The internal copy of libpcre is at version 8.31, which is outdated, buggy and vulnerable. Updating to a more recent version is difficult because glib doesn't contain all the neccessary unicode data tables, see bug 689791 and bug 684222.
The original reason for copying libpcre into glib was that it is patched to use the glib unicode data tables instead of its own. However, it turns out that libgio-2.0 links to libselinux, which in turn links to libpcre. This means that all gtk+/gnome applications actually have two copies of libpcre, more than negating any savings from the shared unicode tables.
So I think we should just drop the embedded pcre copy and always use the system one, and bump the required version to the latest one (8.36).