Upgrade to rustfmt 0.8.0.

Lots of changes this time.

Worked around what looks like a rustfmt bug in parse_inst_operands where
a large match was nested inside Ok().

src/filetest/subtest.rs

@@ -66,7 +66,10 @@ pub trait SubTest {
 /// match 'inst10'.
 impl<'a> filecheck::VariableMap for Context<'a> {
     fn lookup(&self, varname: &str) -> Option<FCValue> {
-        self.details.map.lookup_str(varname).map(|e| FCValue::Regex(format!(r"\b{}\b", e).into()))
+        self.details
+            .map
+            .lookup_str(varname)
+            .map(|e| FCValue::Regex(format!(r"\b{}\b", e).into()))
     }
 }
 
@@ -77,8 +80,7 @@ pub fn run_filecheck(text: &str, context: &Context) -> Result<()> {
         Ok(())
     } else {
         // Filecheck mismatch. Emit an explanation as output.
-        let (_, explain) = checker.explain(&text, context)
-            .map_err(|e| format!("explain: {}", e))?;
+        let (_, explain) = checker.explain(&text, context).map_err(|e| format!("explain: {}", e))?;
         Err(format!("filecheck failed:\n{}{}", checker, explain))
     }
 }