x86-64: Improve GOTPCREL relocation conversion

x86-64: Improve GOTPCREL relocation conversion

When GOTPCREL relocation conversion leads to relocation overflow, we
may get a mysterious linker message, like

relocation truncated to fit: R_X86_64_32S against symbol `foo'

This patch changes the linker message to

failed to convert GOTPCREL relocation; relink with --no-relax

bfd/

	* elf64-x86-64.c (elf_x86_64_convert_load_reloc): Remove the sec
	argument.  Don't check relocation overflow.  Avoid relocation
	overflow if --no-relax is used.  Set converted_reloc on symbol
	if a GOTPCREL relocation is converted.
	(elf_x86_64_relocate_section): Issue a fatal error and suggest
	--no-relax if GOTPCREL relocation conversion leads to relocation
	overflow.
	* elfxx-x86.h (elf_x86_link_hash_entry): Add converted_reloc.

ld/

	* testsuite/ld-x86-64/pr19609-4e.d: Updated.
	* testsuite/ld-x86-64/pr19609-6a.d: Likewise.