hw, asm: Fix encoding/decoding of compares and brz.
asm: Use correct register for ldga in crt0.
llvm: Enable delay slot filling for all calls.
llvm: Update matching of asm constraints to actual API.
llvm: Make sure emergency registers do not live across calls.
llvm: Move guarding of r31 to expansion of pseudos.
sim: Enable simulation without GUI.
bootrom: Keep contents of r0 until halting.
asm, llvm: Use '@' for subtraction of symbols.