Fix -output_mch_path argument to superpmi.py (#44693)

Convert the given path argument to an absolute path. Without this,
the `collect` command changes the current directory before doing its
work, so the file doesn't end up where you expeect it to.

Also, print the given argument in any error message.

src/coreclr/scripts/superpmi.py

@@ -2720,7 +2720,8 @@ def verify_replay_common_args():
  coreclr_args.verify(args,
  "output_mch_path",
  lambda output_mch_path: output_mch_path is None or (not os.path.isdir(os.path.abspath(output_mch_path)) and not os.path.isfile(os.path.abspath(output_mch_path))),
- "Invalid output_mch_path; is it an existing directory or file?")
+ "Invalid output_mch_path \"{}\"; is it an existing directory or file?".format,
+ modify_arg=lambda output_mch_path: None if output_mch_path is None else os.path.abspath(output_mch_path))
 
  coreclr_args.verify(args,
  "merge_mch_files",
@@ -3003,7 +3004,8 @@ def verify_replay_common_args():
  coreclr_args.verify(args,
  "output_mch_path",
  lambda output_mch_path: not os.path.isdir(os.path.abspath(output_mch_path)) and not os.path.isfile(os.path.abspath(output_mch_path)),
- "Invalid output_mch_path; is it an existing directory or file?")
+ "Invalid output_mch_path \"{}\"; is it an existing directory or file?".format,
+ modify_arg=lambda output_mch_path: os.path.abspath(output_mch_path))
 
  coreclr_args.verify(args,
  "pattern",