PR 33455 SEGV in vfinfo at ldmisc.c:527

A reloc howto set up with EMPTY_HOWTO has a NULL name.  More than one
place emitting diagnostics assumes a reloc howto won't have a NULL
name.

	PR 33455
	* coffcode.h (coff_slurp_reloc_table): Don't allow a howto with
	a NULL name.