tools: update elf.h

OpenWrt contains a 2012 copy of glibc's elf.h, which predates the
introduction of some newer architectures like Arm64 and RISC-V.

Linux 5.13 introduced the "gen-hyprel" tool into the kernel compile
(when virtualization/KVM is enabled) which requires EM_AARCH64 to be
defined.

arch/arm64/kvm/hyp/nvhe/gen-hyprel.c: In function 'init_elf':
arch/arm64/kvm/hyp/nvhe/gen-hyprel.c:289:43: error: 'EM_AARCH64'
  undeclared (first use in this function); did you mean 'EM_IA_64'?
  289 |  assert_eq(elf16toh(elf.ehdr->e_machine), EM_AARCH64, "%u");
      |                                           ^~~~~~~~~~

Update the copy of elf.h from the latest glibc to fix this.

Compile-tested: ath79, armvirt, mpc85xx, x86
Run-tested: armvirt

Signed-off-by: Mathew McBride <[email protected]>