Sync crunchide(1) arch support with HEAD

MFC r276764, r281781, r282291, r292106

Add support to crunchide for handling AArch64 (arm64) ELF files.
Remove local EM_* ELF definitions provided by system ELF headers
Restore local EM_AARCH64 constant for bootstrapping
Add RISC-V to supported machine types

Sponsored by: The FreeBSD Foundation