In particular, this incorporates Roman's patches to allow
'make syntax-check' to work on BSD with its exec argv
limitations that previously failed when trying to grep the
large number of files present in libvirt.

cfg.mk needs similar changes, but that will be tackled separately.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>