clif-util: Use anyhow::Error for errors instead of String

Also does the same for `cranelift-filetests`.

cranelift/src/souper_to_peepmatic.rs

@@ -1,20 +1,19 @@
+use anyhow::{Context, Result};
 use std::io::{Read, Write};
 use std::path::Path;
 
-pub fn run(input: &Path, output: &Path) -> Result<(), String> {
+pub fn run(input: &Path, output: &Path) -> Result<()> {
     let peepmatic_dsl = if input == Path::new("-") {
         let stdin = std::io::stdin();
         let mut stdin = stdin.lock();
         let mut souper_dsl = vec![];
         stdin
             .read_to_end(&mut souper_dsl)
-            .map_err(|e| format!("failed to read from stdin: {}", e))?;
-        let souper_dsl =
-            String::from_utf8(souper_dsl).map_err(|e| format!("stdin is not UTF-8: {}", e))?;
-        peepmatic_souper::convert_str(&souper_dsl, Some(Path::new("stdin")))
-            .map_err(|e| e.to_string())?
+            .context("failed to read from stdin")?;
+        let souper_dsl = String::from_utf8(souper_dsl).context("stdin is not UTF-8: {}")?;
+        peepmatic_souper::convert_str(&souper_dsl, Some(Path::new("stdin")))?
     } else {
-        peepmatic_souper::convert_file(input).map_err(|e| e.to_string())?
+        peepmatic_souper::convert_file(input)?
     };
 
     if output == Path::new("-") {
@@ -22,10 +21,10 @@ pub fn run(input: &Path, output: &Path) -> Result<(), String> {
         let mut stdout = stdout.lock();
         stdout
             .write_all(peepmatic_dsl.as_bytes())
-            .map_err(|e| format!("error writing to stdout: {}", e))?;
+            .context("error writing to stdout")?;
     } else {
         std::fs::write(output, peepmatic_dsl.as_bytes())
-            .map_err(|e| format!("error writing to {}: {}", output.display(), e))?;
+            .with_context(|| format!("error writing to {}", output.display()))?;
     }
 
     Ok(())