As mentioned in conda-forge/pot-feedstock#9 (comment) and following up on #130 – always setting CC=g++ is the wrong thing to do, and also always doing the CFLAGS mangling on Mac, regardless of what compilers you're doing/etc, is also the wrong thing to do. This only sets CC on Mac, and allows you to bail out of doing any of this (as e.g. conda-forge will want) by setting POT_LEAVE_CC.

CC @ncourty