configure.ac: enable 64-bit file API where availablie

Without the change scandir() fails on i686-unknown-linux if egl_vendor.d contents contains files with inodes that overflow 32-bit values. In my case it is btrfs:

$ ls -i egl_vendor.d/
5053988166 50_mesa.json

On libEGL.so I see the following symbol change (as reported by nm):

-         U fopen@GLIBC_2.1
-         U fstat@GLIBC_2.33
-         U scandir@GLIBC_2.0
+         U fopen64@GLIBC_2.1
+         U fstat64@GLIBC_2.33
+         U scandir64@GLIBC_2.2

The fix allowed to run 32-bit es2gears_wayland from mesa-demos without failures.