Compilation was failing on systems without memfd_create.
This uses check_c_source_compiles to check whether the memfd_create
function is available on the system.
Credits to Damjan for his help troubleshooting.
Change-Id: I136d9504d7978e3a09438d0d76b2de1042702b2c
Signed-off-by: Pierre Pfister <ppfister@cisco.com>