Fix installing hyperfine

Author: bjorn3

build_system/prepare.rs

@@ -18,7 +18,14 @@ pub(crate) fn prepare(dirs: &Dirs) {
 
     // FIXME maybe install this only locally?
     eprintln!("[INSTALL] hyperfine");
-    Command::new("cargo").arg("install").arg("hyperfine").spawn().unwrap().wait().unwrap();
+    Command::new("cargo")
+        .arg("install")
+        .arg("hyperfine")
+        .env_remove("CARGO_TARGET_DIR")
+        .spawn()
+        .unwrap()
+        .wait()
+        .unwrap();
 
     super::abi_cafe::ABI_CAFE_REPO.fetch(dirs);
     super::tests::RAND_REPO.fetch(dirs);