open-watcom-bin: fix EOVERFLOW on stat() calls

We've already worked around failing stat() calls in the installer by
running it in qemu-user. Turns out on some systems this workaround is
also needed to run `wlib', the archiver of the Open Watcom toolchain.

This issue manifested itself in broken VirtualBox builds due to
/build/virtualbox/out/linux.amd64/dbgopt/obj/VBoxPcBios32/pci32.obj
not being found by `wlib'.

We now just wrap all binaries in qemu-user to avoid this.