add rpath in build.rs because cargo didn't pass crate's args to c…

…urrent project. According to `https://github.com/rust-lang/cargo/issues/5077`

Signed-off-by: HouXiaoxuan <Hou_Xiaoxuan@163.com>

mega/src/build.rs

@@ -4,5 +4,9 @@
 //! 
 
 fn main() -> shadow_rs::SdResult<()> {
+    #[cfg(target_os = "linux")]
+    println!("cargo:rustc-link-arg=-Wl,-rpath,$ORIGIN");
+    #[cfg(target_os = "macos")]
+    println!("cargo:rustc-link-arg=-Wl,-rpath,@executable_path");
     shadow_rs::new()
 }