Currently, `early_error` and `early_warn` in `librustc::session` always use `ColorConfig::Auto`. Modify them to follow the color configuration set by the `--color` option. As colored output is also printed during the early stage, parsing the `--color` option should be done as early as possible. However, there are still some cases when the output needs to be colored before knowing the exact color settings. In these cases, it will be defaulted to `ColorConfig::Auto`, which is the same as before. Fixes #27879.
Encountered an issue with `pacman` while going through the guide for installing the `mingw` toolchain on Windows with `msys2`, after some googling I found the [solution](Alexpux/MSYS2-packages#163 (comment)). I thought it would be good to update the README so people don't get frustrated. r? @steveklabnik