Don't erase all env vars, they are needed on linux

Author: oli-obk

tests/compiletest.rs

@@ -68,7 +68,7 @@ fn run_tests(mode: Mode, path: &str, target: Option<String>) -> Result<()> {
                 std::env::current_dir()?.join("miri").display().to_string(),
                 "cargo".to_string(),
             ],
-            envs: vec![("MIRI_SYSROOT".to_string(), std::env::var("MIRI_SYSROOT").unwrap())],
+            envs: vec![],
         }),
     };
     ui_test::run_tests(config)

ui_test/src/dependencies.rs

@@ -17,8 +17,10 @@ pub fn build_dependencies(config: &Config) -> Result<Vec<(String, PathBuf)>> {
         None => (Path::new("cargo"), &[], &[]),
     };
     let mut build = Command::new(program);
-    build.env_clear();
-    build.env("PATH", std::env::var_os("PATH").unwrap());
+
+    // Avoid poisoning the sysroot and causing unnecessary rebuilds.
+    build.env_remove("RUSTFLAGS");
+
     build.envs(envs.iter().map(|(k, v)| (k, v)));
     build.args(args);
     build.arg("run");