autoconf: Use include-fixed directory with makedepend on newer GCC

On newer GCC releases, the compiler's headers have been split between
the include and include-fixed directories. Add both if the directories
exist.

Signed-off-by: Dan Nicholson <dbn.lists@gmail.com>
Signed-off-by: Julien Cristau <jcristau@debian.org>
1 file changed