four things will affect general binary compatibility:
	CPU architecture and vendor
		initial options:
			i486-pc (any CPU with Intel 80486 microarchitecture)
			x86_64-pc (any CPU with AMD64 or Intel 64 architecture)
			arm*-* (some SoC with a microprocessor implementing some ARM ISA)
		planned future options:
			i586-pc (any CPU with Intel P5 microarchitecture)
			i686-pc (any CPU with Intel P6 or any successive microarchitecture)
			mips*-*
			powerpc*-*
	kernel
		initial options:
			linux
				different hardware targets will be built with different configs
		planned future options:
			knetbsd
	system libraries
		initial options:
			eglibc
				portable C/C++ library: works with almost any kernel
				optimized for speed rather than for space (big and fast)
		planned future options:
			uclibc*
				different configurations of uClibc can be ABI-incompatible
				only works with Linux
				optimized for space rather than for speed (small and slow)
example architecture string:
	x86_64-pc-linux-eglibc