Fix macos build of example

Author: ogoffart

examples/graph/build.rs

@@ -19,7 +19,17 @@ extern crate cpp_build;
 
 fn main() {
     let qt_include_path = std::env::var("DEP_QT_INCLUDE_PATH").unwrap();
-    cpp_build::Config::new()
+    let qt_library_path = std::env::var("DEP_QT_LIBRARY_PATH").unwrap();
+
+    #[allow(unused_mut)]
+    let mut config = cpp_build::Config::new();
+
+    if cfg!(target_os = "macos") {
+        config.flag("-F");
+        config.flag(&qt_library_path);
+    }
+
+    config
         .include(&qt_include_path)
         .include(format!("{}/QtQuick", qt_include_path))
         .include(format!("{}/QtCore", qt_include_path))