These types of rules are not ^C safe:
cc1-checksum.c : cc1-dummy$(exeext) build/genchecksum$(build_exeext)
build/genchecksum$(build_exeext) cc1-dummy$(exeext) > $@
It is a general property that builds are ^C safe, the above changes
retard that feature.
If you output to a temp file, and then mv them to the final file,
they will be (I think) safe.