[Bug preprocessor/103027] Implement warning for homoglyphs in identifiers [CVE-2021-42694]

[dmalcolm at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103027

--- Comment #1 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
I have a work-in-progress patch for this, though it has some issues that need
discussion; I hope to post it soon.