Add regression test for rust-lang#107495

Author: bjorn3

tests/run-make/issue-107495-archive-permissions/foo.rs

@@ -0,0 +1 @@
+

tests/run-make/issue-107495-archive-permissions/rmake.rs

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+extern crate run_make_support;
+
+use run_make_support::{aux_build, out_dir};
+use std::fs;
+#[cfg(unix)]
+use std::os::unix::fs::PermissionsExt;
+use std::path::Path;
+
+fn main() {
+    aux_build().arg("foo.rs").run();
+    verify(&out_dir().join("libfoo.rlib"));
+}
+
+fn verify(path: &Path) {
+    let perm = fs::metadata(path).unwrap().permissions();
+
+    assert!(!perm.readonly());
+
+    // Check that the file is readable for everyone
+    #[cfg(unix)]
+    assert_eq!(perm.mode(), 0o100664);
+}