ld, gold: remove support for -z bndplt (MPX prefix)

bfd/ChangeLog:

	* elf-linker-x86.h (struct elf_linker_x86_params): Remove
	bndplt.
	* elf64-x86-64.c (elf_x86_64_scan_relocs): Ignore
        R_X86_64_PLT32_BND.
	(elf_x86_64_relocate_section): Similarly here.
	(elf_x86_64_link_setup_gnu_properties): Ignore bndplt.
	* elfxx-x86.c: Likewise.
	* elfxx-x86.h: Likewise.

gold/ChangeLog:

	* NEWS: Document -z bndplt.
	* options.h (class General_options): Remove bndplt option.
	* x86_64.cc (class Output_data_plt_x86_64_bnd): Remove.
	(Target_x86_64::do_make_data_plt): Do not use
	Output_data_plt_x86_64_bnd.
	(Target_x86_64::Scan::get_reference_flags): Likewise.
	(Target_x86_64::Scan::check_non_pic): Likewise.
	(Target_x86_64::Scan::local): Likewise.
	(Target_x86_64::Scan::global): Likewise.

ld/ChangeLog:

	* NEWS: Document -z bndplt.
	* emulparams/elf_x86_64.sh: Remove bndplt option.
	* ld.texi: Likewise.
	* testsuite/ld-x86-64/x86-64.exp:
	* testsuite/ld-x86-64/bnd-branch-1-now.d: Removed.
	* testsuite/ld-x86-64/bnd-branch-1.d: Removed.
	* testsuite/ld-x86-64/bnd-branch-1.s: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-1-now.d: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-1.d: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-1.s: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-2-now.d: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-2.d: Removed.
	* testsuite/ld-x86-64/bnd-ifunc-2.s: Removed.
	* testsuite/ld-x86-64/bnd-plt-1-now.d: Removed.
	* testsuite/ld-x86-64/bnd-plt-1.d: Removed.
	* testsuite/ld-x86-64/mpx.exp: Removed.
	* testsuite/ld-x86-64/mpx1.out: Removed.
	* testsuite/ld-x86-64/mpx1a.c: Removed.
	* testsuite/ld-x86-64/mpx1a.rd: Removed.
	* testsuite/ld-x86-64/mpx1b.c: Removed.
	* testsuite/ld-x86-64/mpx1c.c: Removed.
	* testsuite/ld-x86-64/mpx1c.rd: Removed.
	* testsuite/ld-x86-64/mpx2.out: Removed.
	* testsuite/ld-x86-64/mpx2a.c: Removed.
	* testsuite/ld-x86-64/mpx2a.rd: Removed.
	* testsuite/ld-x86-64/mpx2b.c: Removed.
	* testsuite/ld-x86-64/mpx2c.c: Removed.
	* testsuite/ld-x86-64/mpx2c.rd: Removed.
	* testsuite/ld-x86-64/mpx3.dd: Removed.
	* testsuite/ld-x86-64/mpx3a.s: Removed.
	* testsuite/ld-x86-64/mpx3b.s: Removed.
	* testsuite/ld-x86-64/mpx3n.dd: Removed.
	* testsuite/ld-x86-64/mpx4.dd: Removed.
	* testsuite/ld-x86-64/mpx4a.s: Removed.
	* testsuite/ld-x86-64/mpx4b.s: Removed.
	* testsuite/ld-x86-64/mpx4n.dd: Removed.
	* testsuite/ld-x86-64/pr20800a.S: Removed.
	* testsuite/ld-x86-64/pr20800b.S: Removed.
	* testsuite/ld-x86-64/pr21038a-now.d: Removed.
	* testsuite/ld-x86-64/pr21038a.d: Removed.
	* testsuite/ld-x86-64/pr21038a.s: Removed.
	* testsuite/ld-x86-64/pr21038b-now.d: Removed.
	* testsuite/ld-x86-64/pr21038b.d: Removed.
	* testsuite/ld-x86-64/pr21038b.s: Removed.
	* testsuite/ld-x86-64/pr21038c-now.d: Removed.
	* testsuite/ld-x86-64/pr21038c.d: Removed.
	* testsuite/ld-x86-64/pr21038c.s: Removed.