libglib2: the system PCRE needs to have UTF and UCP enabled

If glib2 is compiled with the system PCRE instead of the included
copy, then that system PCRE needs to have support for UTF-8 and
Unicode properties enabled. Otherwise you will get such warnings
at run-time:

GLib-CRITICAL **: PCRE library is compiled without UTF8 support
GLib-CRITICAL **: PCRE library is compiled without UTF8 properties support

Signed-off-by: Sven Neumann <neumann@teufel.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>