gusb/meson.build: pass -DGUSB_COMPILATION to gir compiler
gusb/meson.build: pass -DGUSB_COMPILATION to gir compiler

This fixes cross building of gir using Yocto Project/Buildroot
method.

This is also done on atk with -DATK_COMPILATION and
gdk-pixbuf with -DGDK_PIXBUF_COMPILATION.

hughsie/libgusb,hughsie/libgusb,hughsie/libgusb