C++ Only link against the backend library

For some raison, not all symbols gets exported,
add some dummy code which seems to do the trick

sixtyfps_runtime/corelib/Cargo.toml

@@ -7,8 +7,6 @@ build = "build.rs"
 
 [lib]
 path = "lib.rs"
-crate-type = [ "lib", "cdylib" ]
-
 
 [features]
 # Allow the vewer to query at runtime information about item types

sixtyfps_runtime/corelib/abi/signals.rs

@@ -134,3 +134,14 @@ pub unsafe extern "C" fn sixtyfps_signal_set_handler(
 pub unsafe extern "C" fn sixtyfps_signal_drop(handle: *mut SignalOpaque) {
     core::ptr::read(handle as *mut Signal<()>);
 }
+
+/// Somehow this is required for the extern "C" things to be exported in a dependent dynlib
+#[doc(hidden)]
+pub fn dummy() {
+    #[derive(Clone)]
+    struct Foo;
+    foo(Foo);
+    fn foo(f: impl Clone) {
+        let _ = f.clone();
+    }
+}

sixtyfps_runtime/corelib/layout.rs

@@ -156,3 +156,13 @@ pub extern "C" fn solve_grid_layout(data: &GridLayoutData) {
         }
     }
 }
+
+/// Somehow this is required for the extern "C" things to be exported in a dependent dynlib
+pub fn dummy() {
+    #[derive(Clone)]
+    struct Foo;
+    foo(Foo);
+    fn foo(f: impl Clone) {
+        let _ = f.clone();
+    }
+}

xtask/src/main.rs

@@ -51,7 +51,7 @@ impl CMakeCommand {
 
         let mut target_dir = None;
 
-        let mut params = vec!["-p", "sixtyfps_corelib", "-p", "sixtyfps_rendering_backend_gl"];
+        let mut params = vec!["-p", "sixtyfps_rendering_backend_gl"];
         params.extend(build_params);
 
         let mut first_lib: PathBuf = PathBuf::new();
@@ -59,9 +59,7 @@ impl CMakeCommand {
         run_cargo(&cargo(), "build", &params, |message| {
             match message {
                 Message::CompilerArtifact(ref artifact) => {
-                    if artifact.target.name != "sixtyfps_rendering_backend_gl"
-                        && artifact.target.name != "sixtyfps_corelib"
-                    {
+                    if artifact.target.name != "sixtyfps_rendering_backend_gl" {
                         return Ok(());
                     }