rts: Fix AdjustorPool bitmap manipulation
Previously the implementation of bitmap_first_unset assumed that
__builtin_clz
would accept uint8_t
however it apparently rather
extends its argument to unsigned int
.
To fix this we simply revert to a naive implementation since handling
the various corner cases with clz
is quite tricky. This should be
fine given that AdjustorPool isn't particularly hot. Ideally we would
have a single, optimised bitmap implementation in the RTS but I'll leave
this for future work.
Fixes #21838 (closed).