virglrenderer related -device help failure
Description of problem:
When QEMU is compiled against a recent `virglrenderer` version, running the above command fails like this:
```
$ qemu-system-x86_64 -device virtio-vga-gl,help
qemu-system-x86_64: -device virtio-vga-gl,help: failed to open module: /usr/bin/../lib/qemu/hw-display-virtio-gpu-gl.so: undefined symbol: qemu_egl_display
```
Steps to reproduce:
1. build QEMU against latest `virglrenderer` (1.0.1)
2. run the above command
Additional information:
The cause appears to be related to e8a2db94 cc @marcandre.lureau-rh

Arch only recently updated to latest `virglrenderer` which has exposed the issue.

Note that the device seems to function correctly in normal usage when combined with -display e.g. `-device virtio-vga-gl -display gtk,gl=on`