[NativeAOT-LLVM] Preinitialization test fails

[yowl]

<!-- TODO-LLVM: Fails on Wasm: Assert.AreEqual(unchecked((byte)GetFloat()), FloatConversions.s_byte); -->
<CLRTestTargetUnsupported Condition="'$(IlcMultiModule)' == 'true' or '$(TargetsWasm)' == 'true'">true</CLRTestTargetUnsupported>

[SingleAccretion]

The issue is that our codegen for casts saturates based on the target small type, while (I assume) the correct semantic is to saturate through int. Will confirm this and post a fix as appropriate.