Teach a few targets to resolve BFD_RELOC_8

Teach a few targets to resolve BFD_RELOC_8

and tidy "forward" test.  I've removed some checks in d30v
md_apply_fix that have no business being there.  Any symbol problems
will be caught later in tc_gen_reloc, and overflow checking is done in
gas/write.c.

	* config/tc-d10v.c (md_apply_fix): Apply BFD_RELOC_8.
	* config/tc-pdp11.c (md_apply_fix): Likewise.
	* config/tc-d30v.c (md_apply_fix): Don't emit errors for BFD_RELOC_8,
	BFD_RELOC_16, and BFD_RELOC_64.
	* testsuite/gas/all/gas.exp: Move target exclusions for forward
	test, but not cr16, to..
	* testsuite/gas/all/forward.d: ..here, with explanation.  Remove
	d10v, d30v, and pdp11 xfails.