* acinclude.m4: Determine whether nm support -P and --defined-only.
	* configure.ac: Add TARGET_ to all variables pertaining to target
	that don't have it yet.
	* gentpl.py: Likewise.
	* grub-core/Makefile.am: Likewise.
	* grub-core/genmod.sh.in: Likewise.
	* grub-core/gensyminfo.sh.in: Handle OpenBSD and other non-GNU nm
	as well.