qemu 4.0.0 broken by glib update

In brief, an install CD will successfully boot with qemu 4.0.0 built with glib 2.58.3, but freeze during boot with qemu 4.0.0 built with glib 2.60.0. I tracked it down to glib's GHashTable improvements. qemu is happy with a glib built from
```
 git checkout -f 2.60.4
 git revert --no-edit 86c6f7e2b..3bed8a13b
 git revert --no-edit 75f8ec1df9b48b0c3a13a9125f2c7d7c5adf5159
 git revert --no-edit 603fb5958..d3074a748
 git revert --no-edit 0b45ddc55..0600dd322
```
When the GHashTable improvements were committed, there was already a preemptive note about any breakage being due to using private implementation details, hence mentioning it here rather than with glib.

For the full saga, see: http://gnats.netbsd.org/54310