qemu-keymap is not needed with linux-user, so disable it by default if
tools and system are disabled (tools are disabled by default with linux-user).

Avoid this error with statically linked binaries:

    Linking target qemu-keymap
    /usr/bin/ld: cannot find -lxkbcommon

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-id: 20200824152430.1844159-3-laurent@vivier.eu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>