build-sys: Bump required GLib to 2.44

This will allow usage of `GMutexLocker`. This should be available on
many older distros:

* RHEL 7 - 2.56.1
* RHEL 8 - 2.56.4
* Debian 9 stretch (oldstable) - 2.50.3
* Debian 10 buster (stable) - 2.58.3
* Ubuntu 16.04 xenial - 2.48.2
* Ubuntu 18.04 bionic - 2.56.4

Makefile.am

@@ -31,7 +31,7 @@ AM_CPPFLAGS += -DDATADIR='"$(datadir)"' -DLIBEXECDIR='"$(libexecdir)"' \
 	-DOSTREE_COMPILATION \
 	-DG_LOG_DOMAIN=\"OSTree\" \
   -DOSTREE_GITREV='"$(OSTREE_GITREV)"' \
-	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_40 '-DGLIB_VERSION_MAX_ALLOWED=G_ENCODE_VERSION(2,50)' \
+	-DGLIB_VERSION_MIN_REQUIRED=GLIB_VERSION_2_44 '-DGLIB_VERSION_MAX_ALLOWED=G_ENCODE_VERSION(2,50)' \
 	-DSOUP_VERSION_MIN_REQUIRED=SOUP_VERSION_2_40 '-DSOUP_VERSION_MAX_ALLOWED=G_ENCODE_VERSION(2,48)'
 # For strict aliasing, see https://bugzilla.gnome.org/show_bug.cgi?id=791622
 AM_CFLAGS += -std=gnu99 -fno-strict-aliasing $(WARN_CFLAGS)

configure.ac

@@ -109,7 +109,7 @@ AM_PATH_GLIB_2_0(,,AC_MSG_ERROR([GLib not found]))
 dnl When bumping the gio-unix-2.0 dependency (or glib-2.0 in general),
 dnl remember to bump GLIB_VERSION_MIN_REQUIRED and
 dnl GLIB_VERSION_MAX_ALLOWED in Makefile.am
-GIO_DEPENDENCY="gio-unix-2.0 >= 2.40.0"
+GIO_DEPENDENCY="gio-unix-2.0 >= 2.44.0"
 PKG_CHECK_MODULES(OT_DEP_GIO_UNIX, $GIO_DEPENDENCY)
 
 dnl 5.1.0 is an arbitrary version here