anv: Check if memfd_create is already defined.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103909


Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
(cherry picked from commit 8c1e4b1a)
[Emil Velikov: resolve trivial conflicts]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

Conflicts:
	configure.ac
	meson.build
	src/intel/vulkan/anv_allocator.c