(menu_contentless_cores) Fix mistake - needed to set len to return
value of fill_pathname_join_special
(configuration.c) Fix some unused variable warnings on Linux
syscall -
On older systems, you'll have to include linux/memfd.h for the MFD_ defines, and call memfd_create() via the the syscall(2) wrapper (and include unistd.h and sys/syscall.h for it work). We exclude linux/memfd.h header include because we already provide
the MFD_ defines in case they are missing
