fix: use cfg to allow certain archs certain convs

 (fixes unsupported_fn_ptr_calling_conventions) rust-lang/rust#130260

Author: ElonGaties

src/function.rs

@@ -148,15 +148,32 @@ macro_rules! impl_fn {
     };
 
     (@impl_all ($($nm:ident : $ty:ident),*)) => {
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("Rust")     fn($($ty),*) -> Ret);
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("cdecl")    fn($($ty),*) -> Ret);
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("stdcall")  fn($($ty),*) -> Ret);
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("fastcall") fn($($ty),*) -> Ret);
+        // Universal conventions
+        {
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("Rust")     fn($($ty),*) -> Ret);
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("C")        fn($($ty),*) -> Ret);
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("system")   fn($($ty),*) -> Ret);
+        }
+
+        // x86-specific conventions
+        #[cfg(target_arch = "x86")]
+        {
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("cdecl")    fn($($ty),*) -> Ret);
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("stdcall")  fn($($ty),*) -> Ret);
+            impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("fastcall") fn($($ty),*) -> Ret);
+        }
+
+        // x86_64 Windows
+        #[cfg(all(target_arch = "x86_64", target_os = "windows"))]
         impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("win64")    fn($($ty),*) -> Ret);
+
+        // x86_64 System V (Linux/macOS)
+        #[cfg(all(target_arch = "x86_64", not(target_os = "windows")))]
         impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("sysv64")   fn($($ty),*) -> Ret);
+
+        // ARM conventions
+        #[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
         impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("aapcs")    fn($($ty),*) -> Ret);
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("C")        fn($($ty),*) -> Ret);
-        impl_fn!(@impl_u_and_s ($($nm : $ty),*) ("system")   fn($($ty),*) -> Ret);
     };
 
     (@impl_u_and_s ($($nm:ident : $ty:ident),*) ($call_conv:expr) fn($($param_ty:ident),*) -> $ret:ty) => {