[cmake] Enable color diagnostics

[tbaederr]

Apparently this is the way to do this now (additionally to passing -fcolor-diagnosics?).

See https://cmake.org/cmake/help/latest/envvar/CMAKE_COLOR_DIAGNOSTICS.html.

Result:

Nice. Colors!

[cor3ntin]

On my system (linux, ninja), I do get colors in the current and the doc of cmake seems to imply that the default is to let the compiler does what it does by default.

But i see tons of ninja-related bugs pertaining to colors, and I am not sure they fixed it recently or not.
So i can't tell whether this change is necessary (and how it impacts ci)

[tbaederr]

On my system (linux, ninja), I do get colors in the current and the doc of cmake seems to imply that the default is to let the compiler does what it does by default.

It used to work for me as well IIRC. I have cmake 3.27.7 here and ninja 1.11.1 FWIW.

But i see tons of ninja-related bugs pertaining to colors, and I am not sure they fixed it recently or not. So i can't tell whether this change is necessary (and how it impacts ci)

Yeah I'm also worried about the impact to CI. I do remember some cmake file adding -fcolor-diagnostics to the cflags directly but I can't find it anymore now.

[tbaederr]

I guess we can't do this unconditionally until we require cmake 3.24.