PR25585, PHDR segment not covered by LOAD segment

I closed this bug as invalid, but I think it is worth mentioning in NEWS
that older linkers didn't check PT_PHDR very well.  The patch also allows
people to force an output file with --noinhibit-exec after the error.

bfd/
	PR 25585
	* elf.c (assign_file_positions_for_load_sections): Continue linking
	on "PHDR segment not covered by LOAD segment" errors.
ld/
	PR 25585
	* NEWS: Mention better "PHDR segment not covered by LOAD segment"
	checking.