update `@memcpy` to require equal src and dest lens

* Sema: upgrade operands to array pointers if possible when emitting
   AIR.
 * Implement safety checks for length mismatch and aliasing.
 * AIR: make ptrtoint support slice operands. Implement in LLVM backend.
 * C backend: implement new `@memset` semantics. `@memcpy` is not done
   yet.
edb5e493e6Andrew Kelley committed on 4/25/2023, 6:23:40 PMparenta5c910a
12 files changedLine totals unavailable