standalone: Implement command-line parser using clap

In preparation for adding more command-line options.

@@ -66,1 +67,4 @@
     pub opt_level: OptimizationLevel,
+
+    /// Whether to use LLVM's Legacy Pass Manager.
+    pub legacy_pm: bool,

@@ -894,6 +926,9 @@ impl Nac3 {
             deferred_eval_store: DeferredEvaluationStore::new(),
             llvm_options: CodeGenLLVMOptions {
                 opt_level: OptimizationLevel::Default,
+                // FIXME(Derppening): Add a field to device_db.py for modifying this option

@@ -663,0 +658,4 @@
+            .create_target_machine(self.llvm_options.opt_level)
+            .expect("couldn't create target machine");
+
+        if self.llvm_options.legacy_pm {

@@ -663,0 +663,4 @@
+        let result = main.run_passes("default<O3>", &target_machine, pass_options);
+        if let Err(err) = result {
+            println!("Failed to run optimization for module `main`");
+            println!("{}", err.to_string());

@@ -282,0 +366,4 @@
+            if let Err(err) = result {
+                println!("Failed to run optimization for module `{}`", module.get_name().to_str().unwrap());
+                println!("{}", err.to_string());
+                panic!();

@@ -345,0 +366,4 @@
+    let result = main.run_passes("default<O3>", &target_machine, pass_options);
+    if let Err(err) = result {
+        println!("Failed to run optimization for module `main`");
+        println!("{}", err.to_string());

@@ -663,0 +662,4 @@
+        pass_options.set_merge_functions(true);
+        let result = main.run_passes("default<O3>", &target_machine, pass_options);
+        if let Err(err) = result {
+            panic!("Failed to run optimization for module `main`\n{}", err.to_string());