build: Port from GNOME_DEBUG_CHECK to AX_CHECK_ENABLE_DEBUG
build: Port from GNOME_DEBUG_CHECK to AX_CHECK_ENABLE_DEBUG

The former is deprecated and replaced by the latter. This enables debug
by default for non-release builds.

https://wiki.gnome.org/Projects/GnomeCommon/Migration

https://bugzilla.gnome.org/show_bug.cgi?id=776259

pwithnall/totem-pl-parser,pwithnall/totem-pl-parser