Check for ANSI compliance

[Christian Miller]

Hello,

I use the Emacs compilation mode (M-x compile).

For example, the following "M-x compile RET guix build does-not-exist
RET" would result to the following:

--8<---------------cut here---------------start------------->8---
-*- mode: compilation; default-directory: "~/" -*-
Compilation started at Wed Jan 17 19:18:57

guix build does-not-exist
guix build: error: does-not-exist: unknown package

Compilation exited abnormally with code 1 at Wed Jan 17 19:18:57
--8<---------------cut here---------------end--------------->8---

It is not only visually, but it actually breaks a feature of the mode,
too.  The unknown package error is not detected as an error by the
mode.  I also had a case where it detected warnings as errors.

Could we check for ANSI compliance instead of assuming it's presence?

-- 
Christian Miller