GHDL should respect TERM=dumb

[DanielG]

Description
When running ghdl from within Emacs compilation-mode it is connected to a PTY but TERM=dumb is set to prevent output of escape sequences. GHDL ignores this and so we get garbage displayed. See also #329 which was about essentially the same issue.

Expected behaviour
GHDL should interpret $TERM and output terminal escape sequences appropriate for the specified terminal type. Ideally a system library such as terminfo or perhaps unibilium should be used but simply disabling colors for TERM=dumb should be an easy fix.

How to reproduce?

This prints the error line (and exits with fail) if ghdl output includes an ESC [ sequence despite TERM=dumb.

TERM=dumb script -q -c ghdl >/dev/null 2>&1; ! grep -P '\e\[' typescript

--Daniel