Don't enable Lightbeam tests if Lightbeam isn't enabled.

build.rs

@@ -14,7 +14,11 @@ fn main() {
     let mut out = File::create(out_dir.join("wast_testsuite_tests.rs"))
         .expect("error generating test source file");
 
-    for strategy in &["AlwaysCranelift", "AlwaysLightbeam"] {
+    for strategy in &[
+        "AlwaysCranelift",
+        #[cfg(feature = "lightbeam")]
+        "AlwaysLightbeam",
+    ] {
         writeln!(out, "#[allow(non_snake_case)]").expect("generating tests");
         writeln!(out, "mod {} {{", strategy).expect("generating tests");
 

src/bin/wast.rs

@@ -154,7 +154,10 @@ fn main() {
 
     // Decide how to compile.
     let strategy = match (args.flag_always_lightbeam, args.flag_always_cranelift) {
+        #[cfg(feature = "lightbeam")]
         (true, false) => CompilationStrategy::AlwaysLightbeam,
+        #[cfg(not(feature = "lightbeam"))]
+        (true, false) => panic!("--always-lightbeam given, but Lightbeam support is not enabled"),
         (false, true) => CompilationStrategy::AlwaysCranelift,
         (false, false) => CompilationStrategy::Auto,
         (true, true) => {