sh: Check UNDEFWEAK_NO_DYNAMIC_RELOC

Don't generate dynamic relocation against weak undefined symbol if it
is resolved to zero.  FIXME: UNDEFWEAK_NO_DYNAMIC_RELOC may need to be
checked in more places.

	PR ld/22269
	* elf32-sh.c (allocate_dynrelocs): Discard dynamic relocations
	if UNDEFWEAK_NO_DYNAMIC_RELOC is true.
	(sh_elf_relocate_section): Don't generate dynamic relocation if
	UNDEFWEAK_NO_DYNAMIC_RELOC is true.