Early during mimmutable(2) development, we had a big problem with the

Early during mimmutable(2) development, we had a big problem with the
chrome v8_flags variable's placement in bss, and as a workaround made
it possible to demote a mimmutable mapping's permissions from RW to R.
Further mimmutable-related work in libc's malloc created the same
problem, which led to a better design: objects could be placed into
.openbsd.mutable region, and then at runtime their permission and
immutability could be manipulated better.  So the RW to R demotion
logic is no longer being used, and now this semantic is being deleted.
ok kettenis