properly expose all symbls in manganis without linker intercept (#3230)

* force a volatile read of manganis symbols to preserve them in the final binary

packages/manganis/manganis-macro/src/asset.rs

@@ -104,6 +104,8 @@ impl ToTokens for AssetParser {
 
                         // "/blahcss123.css"
                         bundled: #bundled,
+
+                        metadata: __volatile_reader as fn() -> u8,
                     }
                 }
             ) #option_source

packages/manganis/manganis-macro/src/linker.rs

@@ -17,5 +17,9 @@ pub fn generate_link_section(asset: &impl Serialize) -> TokenStream2 {
         #[link_section = #section_name]
         #[used]
         static ASSET: [u8; #len] = * #asset_bytes;
+
+        fn __volatile_reader() -> u8 {
+            unsafe { std::ptr::read_volatile(ASSET.as_ptr()) }
+        }
     }
 }