sim: introduce {COMPILE,LINK}_FOR_BUILD

sim: introduce {COMPILE,LINK}_FOR_BUILD

These use the same pattern as seen in the opcodes/ dir and in automake
in general (ish).  This helps simplify the boilerplate for building and
linking build-time code, and fixes some inconsistency in flag usage.

For rules that were compiling+linking in a single step, split them into
separate steps so we can apply the correct set of options.  This matches
automake behavior too.