These are marked inline, so building w/gcc at higher optimization
levels will automatically discard them. But building with -O0 will
trigger unused function warnings, so fix that.
The common before/after cover functions in the common mloop generator
are not used by all architecture ports. Doesn't seem to be a hard
requirement, so marking them optional (i.e. unused) is fine.
The cris execute function is conditionally used depending on the
fast-build mode settings, so mark it unused too.
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