Fails to build on OpenBSD 7.0-beta

[jturner]

Myrddin fails to build on OpenBSD 7.0-beta. I was able to get it to
build by creating lib/sys/sys+openbsd:7.0-x64.myr from
sys+openbsd:6.3-x64.myr. However all tests CRASH.

The build fails at:

lib/std/pledge+openbsd.myr:12: type "byte#" incompatible with "byte" near pledge:(byte#, byte## -> int)
FAIL: 6m -O obj -I obj/lib/sys lib/std/pledge+openbsd.myr