build.lua was ISA-centric; add an IRS catalog (ir/<name>) and route it through
the gen / check / test tasks. IR packages have a single-stage generator (gen.odin
emits Odin directly), a plain odin check, and a tests/ suite -- no mnemonic
builders or external-assembler verify, so only those three tasks apply. Purely
additive: the ISA catalog, task functions, and verify-tool probing are untouched.
luajit build.lua --check --test now reports spirv alongside the ISAs
(check ok, test 5 passed).
0f5fa3d1d9