configure: require glib 2.12, 2.20 for mingw32

These are pretty sane requirements to move forward with glib usage.
2.12 is the version found in RHEL/CentOS 5, and 2.20 is the
first version to support g_poll.  Without g_poll, we cannot
integrate well with the glib main loop.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

configure

@@ -1993,13 +1993,21 @@ fi
 
 ##########################################
 # glib support probe
-if $pkg_config --modversion gthread-2.0 > /dev/null 2>&1 ; then
+
+if test "$mingw32" = yes; then
+    # g_poll is required in order to integrate with the glib main loop.
+    glib_req_ver=2.20
+else
+    glib_req_ver=2.12
+fi
+if $pkg_config --atleast-version=$glib_req_ver gthread-2.0 > /dev/null 2>&1
+then
     glib_cflags=`$pkg_config --cflags gthread-2.0 2>/dev/null`
     glib_libs=`$pkg_config --libs gthread-2.0 2>/dev/null`
     LIBS="$glib_libs $LIBS"
     libs_qga="$glib_libs $libs_qga"
 else
-    echo "glib-2.0 required to compile QEMU"
+    echo "glib-$glib_req_ver required to compile QEMU"
     exit 1
 fi