Check if compiler version changed between builds, and if so, start a `clean` job

[fhammerschmidt]

bsb had this feature:

rescript/compiler/bsb/bsb_ninja_regen.ml

Lines 52 to 55 in c738f75

	if check_result = Bsb_bsc_version_mismatch then (
	Bsb_log.warn "@{<info>Different compiler version@}: clean current repo@.";
	Bsb_clean.clean_bs_deps per_proj_dir;
	Bsb_clean.clean_self per_proj_dir);