Take into account all flags when computing iface_hash
The "interface hash" should contain a hash of everything in the
interface file. We are not doing that yet but at least a start is to
include a hash of everything in mi_self_recomp
, rather than just
mi_src_hash
and mi_usages
.
In particular, this fixes #25837 (closed), a bug where we should recompile a
dyn_hi
file but fail to do so.