Add binutils targets for Zephyr RTOS

[stephanosio]

General Workflow

1. Add bfd targets
2. Add gas targets
3. Add ld targets
4. Update ChangeLog(s)

Target Addition Checklist

• bfd
  • aarch64-*-zephyr* -> Same case as aarch64-*-elf*
  • arc-*-zephyr* -> Same case as arc-*-elf*
  • arc64-*-zephyr*
  • arm-*-zephyr* -> Same case as arm-*-eabi*
  • mips-*-zephyr* -> Same case as mips-*-elf*
  • nios2-*-zephyr* -> Handled by nios2-*-*
  • riscv64-*-zephyr* -> Handled by riscv64*-*-*
  • sparc-*-zephyr* -> Handled by sparc*-*-*
  • x86_64-*-zephyr* -> Separate case w/ x86_64_elf64_vec, x86_64_elf32_vec, i386_elf32_vec, iamcu_elf32_vec
  • xtensa-*-zephyr* -> Handled by xtensa*-*-*
• gas -> All cases are handled by *-*-zephyr*
  • aarch64-*-zephyr*
  • arc-*-zephyr*
  • arc64-*-zephyr*
  • arm-*-zephyr*
  • mips-*-zephyr*
  • nios2-*-zephyr*
  • riscv64-*-zephyr*
  • sparc-*-zephyr*
  • x86_64-*-zephyr*
  • xtensa-*-zephyr*
• ld
  • aarch64-*-zephyr*
  • arc-*-zephyr*
  • arc64-*-zephyr*
  • arm-*-zephyr*
  • mips-*-zephyr*
  • nios2-*-zephyr* -> Handled by nios2*-*-*
  • riscv64-*-zephyr* -> Handled by riscv64*-*-*
  • sparc-*-zephyr* -> Handled by sparc*-*-*
  • x86_64-*-zephyr*
  • xtensa-*-zephyr* -> Handled by xtensa*-*-*

NOTE: Zephyr-specific emulations are not implemented for now because we do not currently have finalised Zephyr ABI.

Validation Checklist

• Toolchain Build Test
  • aarch64-*-zephyr*
  • arc-*-zephyr*
  • arc64-*-zephyr*
  • arm-*-zephyr*
  • mips-*-zephyr*
  • nios2-*-zephyr*
  • riscv64-*-zephyr*
  • sparc-*-zephyr*
  • x86_64-*-zephyr*
  • xtensa-*-zephyr*
• Target Compilation Test
  • aarch64-*-zephyr*
  • arc-*-zephyr*
  • arc64-*-zephyr*
  • arm-*-zephyr*
  • mips-*-zephyr*
  • nios2-*-zephyr*
  • riscv64-*-zephyr*
  • sparc-*-zephyr*
  • x86_64-*-zephyr*
  • xtensa-*-zephyr*
• Integration Test
  • aarch64-*-zephyr*
  • arc-*-zephyr*
  • arc64-*-zephyr*
  • arm-*-zephyr*
  • mips-*-zephyr*
  • nios2-*-zephyr*
  • riscv64-*-zephyr*
  • sparc-*-zephyr*
  • x86_64-*-zephyr*
  • xtensa-*-zephyr*

NOTE: The ARC64 support has not been upstreamed yet, so we are omitting arc64-*-zephyr* for now.