Revert "build: build distcheck with --enable-fatal-warnings"
Revert "build: build distcheck with --enable-fatal-warnings"

This reverts commit 8125919b0d8e7c776652e4f1d829b9edfa6c4a68.

This makes things far more annoying than intended, especially since
the list of default warnings isn't consistent from distro to distro.

sir-murray/wayland,mchalupa/wayland,sir-murray/wayland,sir-murray/wayland,mchalupa/wayland,mchalupa/wayland