shared: memfd_create: try MFD_NOEXEC_SEAL

Effective from Linux 6.3 onward, this creates the memfd without execute
permissions and prevents that setting from ever being changed. A
run-time fallback is made to not using MFD_NOEXEC_SEAL when
weston compiled on Linux >= 6.3 is run on Linux < 6.3.

Signed-off-by: Sami Uddin <sami.uddin@astc-design.com>