Fix the test script to return an error if formatting diffs are found.

cranelift/test-all.sh

@@ -27,8 +27,7 @@ function banner {
 # Run rustfmt if we have it.
 banner "Rust formatting"
 if type rustfmt > /dev/null; then
-    # In newer versions of rustfmt, replace --write-mode=diff with --check.
-    if ! "$topdir/format-all.sh" --write-mode=diff ; then
+    if ! "$topdir/format-all.sh" --write-mode=check ; then
         echo "Formatting diffs detected! Run \"cargo fmt --all\" to correct."
         exit 1
     fi

lib/codegen/src/write.rs

@@ -148,12 +148,7 @@ fn write_preamble(
 //
 // Basic blocks
 
-fn write_arg(
-    w: &mut Write,
-    func: &Function,
-    regs: Option<&RegInfo>,
-    arg: Value,
-) -> fmt::Result {
+fn write_arg(w: &mut Write, func: &Function, regs: Option<&RegInfo>, arg: Value) -> fmt::Result {
     write!(w, "{}: {}", arg, func.dfg.value_type(arg))?;
     let loc = func.locations[arg];
     if loc.is_assigned() {