Updating arch support for arm

[Petermarcu]

This adds support for arm and arm64 rids to address https://github.com/dotnet/core-setup/issues/4081

[Petermarcu]

I haven't been able to build and test locally on different arch's so marking this a no merge.

[eerhardt]

LGTM.

It looks like the host already has the correct code for ARM architectures, so we should be good there:

core-setup/src/corehost/common/utils.cpp

Lines 187 to 200 in 4b628f4

	const pal::char_t* get_arch()
	{
	#if _TARGET_AMD64_
	return _X("x64");
	#elif _TARGET_X86_
	return _X("x86");
	#elif _TARGET_ARM_
	return _X("arm");
	#elif _TARGET_ARM64_
	return _X("arm64");
	#else
	#error "Unknown target"
	#endif
	}

[Petermarcu]

Finished verifying this on my Pi and confirmed we now have the correct behavior.