Update GCC version

[snej]

I tried to use this to build my project, but I use some C++20 features including the new comparison (<=>) operator, which GCC 9 doesn’t support. So I got a “no such file” error on #include <compare>.

GCC 10 does build my project successfully on Linux. I’m just trying to find a way to do this build on macOS. So it would be nice if you updated to a newer version of GCC.