difftest: fix use-installed-tools feature

Author: Firestar99

Cargo.toml

@@ -54,7 +54,7 @@ rustc_codegen_spirv-types = { path = "./crates/rustc_codegen_spirv-types", versi
 rustc_codegen_spirv-target-specs = { path = "crates/rustc_codegen_spirv-target-specs", version = "=0.9.0" }
 
 # difftest libraries mirrored from difftest workspace
-difftest-runner = { path = "tests/difftests/runner" }
+difftest-runner = { path = "tests/difftests/runner", default-features = false }
 
 # External dependencies that need to be mentioned more than once.
 tracing = "0.1"

tests/difftests/runner/src/runner.rs

@@ -634,6 +634,10 @@ impl Runner {
 
 pub fn forward_features(cmd: &mut Command) {
     cmd.arg("--features");
+    #[cfg(all(feature = "use-compiled-tools", feature = "use-installed-tools"))]
+    compile_error!(
+        "Features `use-compiled-tools` and `use-installed-tools` are mutually exclusive"
+    );
     #[cfg(feature = "use-compiled-tools")]
     {
         cmd.arg("difftest/use-compiled-tools");