gold: Handle R_X86_64_CODE_4_GOTPCRELX

gold: Handle R_X86_64_CODE_4_GOTPCRELX

Handle R_X86_64_CODE_4_GOTPCRELX and convert

	mov	name@GOTPCREL(%rip), %r31

to

	lea	name@GOTPCREL(%rip), %r31

if the instruction is encoded with the REX2 prefix when possible.

elfcpp/

	* x86_64.h (R_X86_64_CODE_4_GOTPCRELX): New.

gold/

	* x86_64.cc (Target_x86_64::can_convert_mov_to_lea): Handle
	R_X86_64_CODE_4_GOTPCRELX.
	(Target_x86_64::Scan::get_reference_flags): Likewise.
	(Target_x86_64::Scan::local): Likewise.
	(Target_x86_64::Scan::possible_function_pointer_reloc): Likewise.
	(Target_x86_64::Scan::global): Likewise.
	(Target_x86_64::Relocate::relocate): Likewise.
	* testsuite/x86_64_mov_to_lea1.s: Add a test for
	R_X86_64_CODE_4_GOTPCRELX.
	* testsuite/x86_64_mov_to_lea2.s: Likewise.
	* testsuite/x86_64_mov_to_lea3.s: Likewise.
	* testsuite/x86_64_mov_to_lea4.s: Likewise.
	* testsuite/x86_64_mov_to_lea5.s: Likewise.
	* testsuite/x86_64_mov_to_lea.sh: Updated.