mingw: set $env:TERM=xterm-256color for newer OSes

For windows builds >= 15063 set $env:TERM to xterm-256color because they
have a more capable console system that supports this. Also set
$env:COLORTERM=truecolor if unset.

See #3629 regarding problems caused by always setting
$env:TERM=cygwin.

This is the same heuristic used by the Cygwin runtime.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

Author: rkitover

compat/mingw.c

@@ -3401,9 +3401,22 @@ static void setup_windows_environment(void)
 		convert_slashes(tmp);
 	}
 
-	/* simulate TERM to enable auto-color (see color.c) */
-	if (!getenv("TERM"))
-		setenv("TERM", "cygwin", 1);
+
+	/*
+	 * Make sure TERM is set up correctly to enable auto-color
+	 * (see color.c .) Use "cygwin" for older OS releases which
+	 * works correctly with MSYS2 utilities on older consoles.
+	 */
+	if (!getenv("TERM")) {
+		if (windows_build() >= 15063) {
+			setenv("TERM", "xterm-256color", 1);
+
+			if (!getenv("COLORTERM"))
+				setenv("COLORTERM", "truecolor", 1);
+		}
+		else
+			setenv("TERM", "cygwin", 1);
+	}
 
 	/* calculate HOME if not set */
 	if (!getenv("HOME")) {