Do not override CFLAGS, as CFLAGS is a user flag.

* Furthermore, use NDEBUG globally to detect the presence
  of building with more debug output information.
  AX_CHECK_ENABLE_DEBUG is easier to use, and nowadays
  Gnome has also switched to it from its own custom solution.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
10 files changed