Add support for ARM64EC

[dpaoliello]

Arm64EC is a new ABI for Windows binaries that is designed to improve performance of emulated x64 apps on ARM64 devices: https://learn.microsoft.com/en-us/windows/arm/arm64ec

Within the COFF and PE formats, there is a new IMAGE_FILE_MACHINE_ARM64EC enum set to 0xA641: https://github.com/llvm/llvm-project/blob/3d1172813fc640514c6cb421394c34f4b42cb634/llvm/include/llvm/BinaryFormat/COFF.h#L101

For relocations, Arm64EC is treated the same as AArch64.

I also updated the round-trip test for COFF to run for all supported architectures.

[philipc]

This is an ABI, not an architecture, and for the purposes of this crate the only thing it affects is the machine field in the header, so I'm reluctant to add this as a separate architecture. We can if you think it's the best choice, but alternatives to consider are:

• add Object::set_coff_machine
• add a machine field to FileFlags::Coff (although this is a breaking change)
• add Object:::set_subarchitecture and add a new SubArchitecture enum (because LLVM uses Triple::aarch64 with Triple::AArch64SubArch_arm64ec)

[dpaoliello]

@philipc I like the idea of using a sub-architecture to match LLVM.

Question about the design though, should this be unified with Object::set_macho_cpu_subtype, or leave them separate for now?

[philipc]

Thanks!

[dpaoliello]

@philipc can we please get a new release that contains this change?

[philipc]

Released 0.32.2