treewide: memfd_create: use exec flags

treewide: memfd_create: use exec flags

Use the flags MEMFD_EXEC or MEMFD_NOEXEC_SEAL as applicable.

These warnings instruct the kernel wether the memfd is executable or
not.

Without specifying those flags the kernel will emit the following
warning since version 6.3,
commit 105ff5339f49 ("mm/memfd: add MFD_NOEXEC_SEAL and MFD_EXEC"):

    kernel: memfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=1 'systemd'