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.