[ArgumentPromotion] Bail if any callers are minsize

Argument promotion mostly works on functions with more than one caller (otherwise the function would be inlined or is dead), so there's a good chance that performing this increases code size since we introduce loads at every call site. If any caller is marked minsize, bail.

We could compare the number of loads/stores removed from the function with the number of loads introduced in callers, but that's TODO.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D149768