List of env vars recognized by cg_clif

CG_CLIF_JIT_ARGS: When JIT mode is enable pass these arguments to the program.
CG_CLIF_INCR_CACHE_DISABLED: Don't cache object files in the incremental cache. Useful during development of cg_clif to make it possible to use incremental mode for all analyses performed by rustc without caching object files when their content should have been changed by a change to cg_clif.
CG_CLIF_DISPLAY_CG_TIME: If "1", display the time it took to perform codegen for a crate