This will cause noise and CPU overhead on incremental builds.
Especially with make it is quite a bit slower. On my local setup I don't
need/want the translations to be installed anyway.
Especially with projects having few targets, this speeds incremental
build up by a large portion.
This should not be relevant for packaging, but due to the little
complexity of the new option I consider it a nonissue.

Because the same option should be respected by ki18n and kdoctools, the
"KF_" prefix is used instead of "ECM_".