Don't generate PLT relocations for now binding

Don't generate PLT relocations for now binding

There is no need for PLT relocations with -z now. We can use GOT
relocations, which take less space, instead and replace 16-byte .plt
entres with 8-byte .plt.got entries.

bfd/

	* elf32-i386.c (elf_i386_check_relocs): Create .plt.got section
	for now binding.
	(elf_i386_allocate_dynrelocs): Use .plt.got section for now
	binding.
	* elf64-x86-64.c (elf_x86_64_check_relocs): Create .plt.got
	section for now binding.
	(elf_x86_64_allocate_dynrelocs): Use .plt.got section for now
	binding.

ld/testsuite/

	* ld-i386/i386.exp: Run PR ld/17689 tests with -z now.
	* ld-x86-64/x86-64.exp: Likewise
	* ld-i386/pr17689now.rd: New file.
	* ld-x86-64/pr17689now.rd: Likewise