config: replace deprecated AM_CONFIG_HEADER with AC_CONFIG_HEADERS
config: replace deprecated AM_CONFIG_HEADER with AC_CONFIG_HEADERS

Signed-off-by: Gaetan Nadon <8a8cc541338200f67d4d0bcb65c78b6166649462@videotron.ca>

fgouget/xf86-video-qxl,dezelin/xf86-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,facboy/xserver-xorg-video-qxl,dezelin/xf86-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl,sombrafam/virtioqxl-xf86-video-qxl,dezelin/xf86-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl