[run-time] Disable allocation counts when not using MPS.

This is really needing to target HARP vs others, because the
GC TEB isn't configured correctly in non-HARP run-times.
[rt] Start calling the MPS-style API.
[rt] Map prim_allocate_filled to new API.
[rt,c] Switch more things over to the collector APIs.
[crt] Use GC_MALLOC_ATOMIC where possible.
[rt] Finish calling MPS-style API.
[rt] Call MPS-style API in posix-threads