Remove target dependent CPP for Word64/Int64 (#11470)

Primops types were dependent on the target word-size at *compiler*
compilation time. It's an issue for multi-target as GHC may not have the
correct primops types for the target.

This patch fixes some primops types: if they take or return fixed 64-bit
values they now always use `Int64#/Word64#`, even on 64-bit
architectures (where they used `Int#/Word#` before). Users of these
primops may now need to convert from Int64#/Word64# to Int#/Word# (a
no-op at runtime).

This is a stripped down version of !3658 which goes the all way of
changing the underlying primitive types of Word64/Int64. This is left
for future work.

T12545 allocations increase ~4% on some CI platforms and decrease ~3% on
AArch64.

Metric Increase:
    T12545

Metric Decrease:
    T12545