compiletest: Give a better error message if node isn't installed

Author: jyn514

src/tools/compiletest/src/runtest.rs

@@ -2135,15 +2135,15 @@ impl<'test> TestCx<'test> {
             if let Some(ref p) = self.config.nodejs {
                 args.push(p.clone());
             } else {
-                self.fatal("no NodeJS binary found (--nodejs)");
+                self.fatal("emscripten target requested and no NodeJS binary found (--nodejs)");
             }
         // If this is otherwise wasm, then run tests under nodejs with our
         // shim
         } else if self.config.target.contains("wasm32") {
             if let Some(ref p) = self.config.nodejs {
                 args.push(p.clone());
             } else {
-                self.fatal("no NodeJS binary found (--nodejs)");
+                self.fatal("wasm32 target requested and no NodeJS binary found (--nodejs)");
             }
 
             let src = self