libpcre: enable unicode properties by default

libpcre: enable unicode properties by default

Enable Unicode properties by default, as they're useful and for example GLib
needs them.  As there is an impact to code size add this as a PACKAGECONFIG so
tightly constrained environments can save space by potentially disabling them.

Also change --enable-utf8 to --enable-utf, as the former is a compatibility
option for the latter.

Signed-off-by: Ross Burton <ross.burton@intel.com>