Fix cpu segfault (#1488)

* fix cpu segfault

* nit in tests

mlx/compile_impl.h

@@ -6,6 +6,20 @@
 
 namespace mlx::core::detail {
 
-bool compile_available_for_device(const Device& device);
+// This is not part of the general C++ API as calling with a bad id is a bad
+// idea.
+std::function<std::vector<array>(const std::vector<array>&)> compile(
+    const std::function<std::vector<array>(const std::vector<array>&)>& fun,
+    std::uintptr_t fun_id,
+    bool shapeless = false,
+    std::vector<uint64_t> constants = {});
 
-}
+// Erase cached compile functions
+void compile_erase(std::uintptr_t fun_id);
+
+// Clear the compiler cache causing a recompilation of all compiled functions
+// when called again.
+void compile_clear_cache();
+
+bool compile_available_for_device(const Device& device);
+} // namespace mlx::core::detail