[x86-64] Omit dynamic sections symbols

[x86-64] Omit dynamic sections symbols

Define elf_backend_omit_section_dynsym to bfd_true for x86-64, similar
to i386, x86-64 doesn't need dynamic sections symbols.

bfd/

	* elf64-x86-64.c (elf_backend_omit_section_dynsym): New.  Defined
	to bfd_true.

ld/

	* testsuite/ld-ifunc/ifunc-1-local-x86.d: Updated.
	* testsuite/ld-ifunc/ifunc-1-x86.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-local-x86-64.d: Likewise.
	* testsuite/ld-ifunc/ifunc-2-x86-64.d: Likewise.
	* testsuite/ld-ifunc/ifunc-3a-x86.d: Likewise.
	* testsuite/ld-ifunc/pr17154-x86-64.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-1.d: Likewise.
	* testsuite/ld-x86-64/bnd-ifunc-2.d: Likewise.
	* testsuite/ld-x86-64/bnd-plt-1.d: Likewise.
	* testsuite/ld-x86-64/ilp32-4-nacl.d: Likewise.
	* testsuite/ld-x86-64/ilp32-4.d: Likewise.
	* testsuite/ld-x86-64/load1c-nacl.d: Likewise.
	* testsuite/ld-x86-64/load1c.d: Likewise.
	* testsuite/ld-x86-64/load1d-nacl.d: Likewise.
	* testsuite/ld-x86-64/load1d.d: Likewise.
	* testsuite/ld-x86-64/pr14207.d: Likewise.
	* testsuite/ld-x86-64/pr19162.d: Likewise.
	* testsuite/ld-x86-64/tlsdesc-nacl.rd: Likewise.
	* testsuite/ld-x86-64/tlsdesc.rd: Likewise.
	* testsuite/ld-x86-64/tlsgdesc-nacl.rd: Likewise.
	* testsuite/ld-x86-64/tlsgdesc.rd: Likewise.
	* testsuite/ld-x86-64/tlspic-nacl.rd: Likewise.
	* testsuite/ld-x86-64/tlspic.rd: Likewise.