Fix clippy warnings

src/command/build.rs

@@ -21,7 +21,7 @@ use std::io::Write;
 use std::path::Path;
 
 pub fn build(target: &Target, in_file: &Path, out_file: &Path) -> Result<(), String> {
-    let mut buf = Box::new(Vec::new());
+    let mut buf = Box::<Vec<u8>>::default();
     build_to_buffer(target, in_file, &mut buf)?;
 
     if out_file.to_str() == Some("-") {

src/command/run.rs

@@ -22,7 +22,7 @@ use std::process::Command;
 use std::process::Stdio;
 
 pub fn run(target: Target, in_file: PathBuf) -> Result<(), String> {
-    let mut buf = Box::new(Vec::new());
+    let mut buf = Box::<Vec<u8>>::default();
     build::build_to_buffer(&target, &in_file, &mut buf)?;
 
     match target {

src/generator/qbe.rs

@@ -270,7 +270,7 @@ impl QbeGenerator {
                 func.assign_instr(
                     tmp.clone(),
                     qbe::Type::Word,
-                    qbe::Instr::Copy(qbe::Value::Const(if *literal { 1 } else { 0 })),
+                    qbe::Instr::Copy(qbe::Value::Const(u64::from(*literal))),
                 );
 
                 Ok((qbe::Type::Word, tmp))