[llvm] [ADT] Add signed and unsigned mulHi and mulLo to APInt (PR #84719)

[Simon Pilgrim via llvm-commits]

================
@@ -3094,3 +3094,19 @@ void llvm::LoadIntFromMemory(APInt &IntVal, const uint8_t *Src,
     memcpy(Dst + sizeof(uint64_t) - LoadBytes, Src, LoadBytes);
   }
 }
+
+APInt APIntOps::mulhs(const APInt &C1, const APInt &C2) {
+  assert(C1.getBitWidth() >= C2.getBitWidth());
----------------
RKSimon wrote:

(style) Assertions should include a message string as well:
```
assert(C1.getBitWidth() >= C2.getBitWidth() && "BitWidth mismatch");
```

https://github.com/llvm/llvm-project/pull/84719