Remove .eh_frame zero terminators

Remove .eh_frame zero terminators

The machinery to do this was there, but not enabled if the terminator
was the only thing in the section.

bfd/
	* elf-eh-frame.c (_bfd_elf_parse_eh_frame): Don't exit early
	for a section containing just a terminator.  Allow multiple
	terminators at end of section.
	* elflink.c (bfd_elf_discard_info): Iterate over .eh_frame
	sections when not adding alignment.  Assert on terminator in
	the middle of FDEs.
ld/
	* testsuite/ld-elf/eh3.d: Update.
	* testsuite/ld-elf/eh4.d: Update.