libglib2: bump to version 2.48.0

libglib2: bump to version 2.48.0

Switch to system/unbundled pcre since it's the default and recommended
by upstream now.
It's also good security practice since pcre patches won't get updated in
the bundled version inside glib so often.

As stated in glib's NEWS:

Overview of changes in GLib 2.47.5

* the system copy of PCRE is now used by default to implement GRegex.
  Configure with --with-pcre=internal if a system PCRE version
  is unavailable or undesired.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>