Use GNU AR for illumos (#585)

Author: smklein

src/lib.rs

@@ -2342,6 +2342,12 @@ impl Build {
                 Some(t) => return Ok((t, "lib.exe".to_string())),
                 None => "lib.exe".to_string(),
             }
+        } else if target.contains("illumos") {
+            // The default 'ar' on illumos uses a non-standard flags,
+            // but the OS comes bundled with a GNU-compatible variant.
+            //
+            // Use the GNU-variant to match other Unix systems.
+            "gar".to_string()
         } else if self.get_host()? != target {
             match self.prefix_for_target(&target) {
                 Some(p) => {