glib-compat: fix problems with not-quite glib 2.22

glib-compat: fix problems with not-quite glib 2.22

Commit 89b516d8b9444ece8ccabb322a9389587c7a7b83 ("glib: add
compatibility interface for g_get_monotonic_time()") aimed
at making qemu build with old glib versions. At least SLES11SP3,
however, contains a backport of g_get_monotonic_time() while
keeping the reported glib version at 2.22.

Let's work around this by a strategically placed #define.

Signed-off-by: Cornelia Huck <[email protected]>
Message-id: 1427987865[email protected]
Signed-off-by: Peter Maydell <[email protected]>