Partially revert "Make build matrix output a bit nicer."

I have found a better solution.

The change to check/cross sign is not reverted.

This partially reverts commit 3797d4eb036f08b349c457fc69ae625c8534409d.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
build-matrix: use $(newline) instead of ; to enter command

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