Unconditionally enable sse3, ssse3, and sse4.1 when fuzzing

This commit unconditionally enables some x86_64 instructions when
fuzzing because the cranelift backend is known to not work if these
features are disabled. From discussion on the wasm simd proposal the
assumed general baseline for running simd code is SSE4.1 anyway.

At this time I haven't added any sort of checks in Wasmtime itself.
Wasmtime by default uses the native architecture and when explicitly
enabling features this still needs to be explicitly specified.

Closes bytecodealliance#3809

crates/fuzzing/src/generators.rs

@@ -699,9 +699,16 @@ impl<'a> Arbitrary<'a> for CodegenSettings {
             if u.ratio(1, 10)? {
                 let flags = target_features! {
                     test: is_x86_feature_detected,
-                    std:"sse3" => clif:"has_sse3",
-                    std:"ssse3" => clif:"has_ssse3",
-                    std:"sse4.1" => clif:"has_sse41",
+
+                    // These features are considered to be baseline required by
+                    // Wasmtime. Currently SIMD some simd code generation will
+                    // fail if these features are disabled, so unconditionally
+                    // enable them as we're not interested in fuzzing without
+                    // them.
+                    std:"sse3" => clif:"has_sse3" ratio: 1 in 1,
+                    std:"ssse3" => clif:"has_ssse3" ratio: 1 in 1,
+                    std:"sse4.1" => clif:"has_sse41" ratio: 1 in 1,
+
                     std:"sse4.2" => clif:"has_sse42",
                     std:"popcnt" => clif:"has_popcnt",
                     std:"avx" => clif:"has_avx",