Separate out native-only packages in build matrix (& cosmetics)

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Correct typo "MinGW 3x"

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Update package stats in "Supported Toolchains" table

Signed-off-by: Timothy Gu <timothygu99@gmail.com>