[llvm] [WebAssembly] Fix lowering of (extending) loads from addrspace(1) globals (PR #155937)

[via llvm-commits]

QuantumSegfault wrote:

Okay. `reduceLoadWidth` doesn't work because `isLegalNarrowLdSt` on line 15539 returns false, because of this starting line 6915
```cpp
if (LegalOperations &&
        !TLI.isLoadExtLegal(ExtType, Load->getValueType(0), MemVT))
      return false;
```

It all comes down to the same: `!isLoadExtLegal` :/

Not sure what to do about it.

https://github.com/llvm/llvm-project/pull/155937