Include error information on error opening output file

[guest271314]

Fixes #2740

[guest271314]

@sbc100 Want to take a look at this; make edits, etc. I don't think the linter likes this string adjacent to string pattern

 ERROR("unable to open %s for writing: WABT tools do not create directories\n"
      "when they don't exist in path passed to -o\n", filename_str.c_str());

[sbc100]

Perhaps update the PR description to be "Include error information on error opening output file"