bfd ASSOCIATED_VECS

Tidy code setting ASSOCIATED_VECS, which could be fooled by unusual
configure options such as --enable-targets="srec,all".

	* targets.c (_bfd_associated_vector): Remove comma after
	ASSOCIATED_VECS.
	* configure.ac: Set assocvecs from targ_defvec and
	targ_selvecs when handling the target, rather than assuming
	those variables are still set for the target when handling
	--enable-targets=all.  Move code making assocvecs unique
	later.  Do so in a way that need not run sed afterwards, and
	leave a trailing comma.
	* configure: Regenerate.