Provide a default empty implementation for the LLVMCallbacks trait.

Author: nlewycky

lib/llvm-backend-tests/tests/compile.rs

@@ -33,10 +33,6 @@ impl LLVMCallbacks for RecordPreOptIR {
     fn preopt_ir_callback(&mut self, module: &InkwellModule) {
         self.preopt_ir = module.print_to_string().to_string();
     }
-
-    fn postopt_ir_callback(&mut self, _: &InkwellModule) {}
-
-    fn obj_memory_buffer_callback(&mut self, _: &InkwellMemoryBuffer) {}
 }
 
 #[test]

lib/llvm-backend/src/lib.rs

@@ -37,9 +37,9 @@ pub type InkwellModule<'ctx> = inkwell::module::Module<'ctx>;
 pub type InkwellMemoryBuffer = inkwell::memory_buffer::MemoryBuffer;
 
 pub trait LLVMCallbacks: std::any::Any + 'static {
-    fn preopt_ir_callback(&mut self, module: &InkwellModule);
-    fn postopt_ir_callback(&mut self, module: &InkwellModule);
-    fn obj_memory_buffer_callback(&mut self, memory_buffer: &InkwellMemoryBuffer);
+    fn preopt_ir_callback(&mut self, _module: &InkwellModule) {}
+    fn postopt_ir_callback(&mut self, _module: &InkwellModule) {}
+    fn obj_memory_buffer_callback(&mut self, _memory_buffer: &InkwellMemoryBuffer) {}
 }
 
 pub struct LLVMBackendConfig {