fix process=interpret build for 'arch=arm64 platform=ios'
make sure binary-to-object doesn't generate empty objects for invalid format/architecture combinations
correct THREAD_STATE_THREAD register for arm64 on darwin
Merge pull request #378 from joshuawarner32/arm64-interpret-ios

Add support for 'platform=ios arch=arm64 process=interpret' build
work in progress towards 64-bit ARM JIT support

This won't build, it's just a snapshot of what I have so far.

Conflicts:
	include/avian/codegen/architecture.h
	include/avian/codegen/registers.h
	src/codegen/compiler.cpp
	src/codegen/compiler/event.cpp
	src/codegen/compiler/site.cpp
	src/codegen/compiler/site.h
	src/codegen/registers.cpp
	src/codegen/target/arm/assembler.cpp
	src/codegen/target/arm/registers.h
snapshot of ARM64 instruction encoding work

Still not building, but more progress.