Also set SDKROOT when building apple platforms (#1475)

Author: chyyran

src/lib.rs

@@ -2742,6 +2742,8 @@ impl Build {
 
             cmd.args.push("-isysroot".into());
             cmd.args.push(OsStr::new(&sdk_path).to_owned());
+            cmd.env
+                .push(("SDKROOT".into(), OsStr::new(&sdk_path).to_owned()));
 
             if target.abi == "macabi" {
                 // Mac Catalyst uses the macOS SDK, but to compile against and