Cranelift only has one instruction SIMD which depends on SSE4.2 so this
commit adds a lowering rule for `pcmpgtq` which doesn't use SSE4.2 and
enables lowering the baseline requirement for SIMD support from SSE4.2
to SSE4.1.
The `has_sse42` setting is no longer enabled by default for Cranelift.
Additionally `enable_simd` no longer requires `has_sse42` on x64.
Finally the fuzz-generator for Wasmtime codegen settings now enables
flipping the `has_sse42` setting instead of unconditionally setting it
to `true`.
The specific lowering for `pcmpgtq` is copied from LLVM's lowering of
this instruction.
2d25db047f