Additional test. Getting test #2 to work is the current target.
I need to make .elf.asm tests compare their execution outputs,
not binaries.

Started putting this all together. First step on this road:
getting full AST generated. Second step: per instruction code
generation. Third step: ELF object file output. Fourth step
(not really a priority right now): raw binary file output;
this one will require some serious shenanigans in code generation.