d92204c900 build: add warning to detect hidden copies in range-for loops (Cory Fields)
466e16e0e8 cleanup: avoid hidden copies in range-for loops (Cory Fields)
Pull request description:
Following-up on #13241, which was itself a follow-up of #12169.
See title. Fixing these would otherwise be a continuous process, adding the warning should keep them from cropping up.
Note that the warning seems to be Clang-only for now.
Tree-SHA512: ccfb769c3128b3f92c95715abcf21ee2496fe2aa384f80efead1529a28eeb56b98995b531b49a089f8142601389e63f7bb935963d724eacde4f5e1b4a024934b