package/pkg-cmake: disable colouring the output

cmake is the only build-system we support that does colour its output,

Also, since parallel builds generates intermixed output lines, it makes
for ugly-looking output.

Just disable cmake colouring globally.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>