[Issue 21266] Improve TTY and color detection in build.d

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21266

Walter Bright <bugzilla at digitalmars.com> changed:

           What    |Removed                     |Added
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           Keywords|                            |TestSuite
                 CC|                            |bugzilla at digitalmars.com

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