configure: Add AC_SYS_LARGEFILE for mmap64 support on 64-bit

Without enabling largefile support the prototype for mmap64() is broken
on Linux/x86_64 with the result being a 32-bit integer sign-extended
to fill a 64-bit pointer. Hilarity ensues.

tests/gem_fence_thrash.c

@@ -75,6 +75,7 @@ bo_create (int fd)
 	tiling.stride = 1024;
 	ret = ioctl(fd, DRM_IOCTL_I915_GEM_SET_TILING, &tiling);
 	assert(ret == 0);
+	assert(tiling.tiling_mode == I915_TILING_X);
 
 	memset(&mmap_arg, 0, sizeof(mmap_arg));
 	mmap_arg.handle = handle;