Propagate clang-format failure from reformat-formatted-files

Specifically, this allows to manually terminate a (long-running)
reformat-formatted-files through Ctrl-C.

Change-Id: Ic44099b29e72619a6697d349a611a12b8536a3bf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100154
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

solenv/clang-format/reformat-formatted-files

@@ -42,7 +42,7 @@ foreach my $filename (@filenames)
     print($filename . "\n");
     if (!$dry_run)
     {
-        system($command);
+        system($command) == 0 or die "failed to execute \"$command\": $?";
     }
 }