bug#28242: Batch mode compiling: Error messages are displayed with "invalid character" glyph bounding symbols.

[Glenn Morris]

If your system has the same issue with gcc warnings (and if you choose
not to answer the question, a cynic like me will assume it does), then
your system is misconfigured, and it's not important to improve Emacs's
support for it.

Don't set LANG to a UTF8 locale if your font doesn't support it.
gcc went through the same issue years ago. Eg

https://stackoverflow.com/questions/6537520/strange-characters-present-in-gcc-compilation-output-message-on-console