fails to build with older libc: F_GET_SEALS etc. undefined

building weston fails with:

../weston-8.0.0/shared/os-compatibility.c: In function 'os_ro_anonymous_file_get_fd':
../weston-8.0.0/shared/os-compatibility.c:343:26: error: 'F_GET_SEALS' undeclared (first use in this function)
../weston-8.0.0/shared/os-compatibility.c:343:26: note: each undeclared identifier is reported only once for each function it appears in
../weston-8.0.0/shared/os-compatibility.c:41:25: error: 'F_SEAL_SHRINK' undeclared (first use in this function)
../weston-8.0.0/shared/os-compatibility.c:349:15: note: in expansion of macro 'READONLY_SEALS'
../weston-8.0.0/shared/os-compatibility.c:41:41: error: 'F_SEAL_GROW' undeclared (first use in this function)
../weston-8.0.0/shared/os-compatibility.c:349:15: note: in expansion of macro 'READONLY_SEALS'
../weston-8.0.0/shared/os-compatibility.c:41:55: error: 'F_SEAL_WRITE' undeclared (first use in this function)
../weston-8.0.0/shared/os-compatibility.c:349:15: note: in expansion of macro 'READONLY_SEALS'
../weston-8.0.0/shared/os-compatibility.c: In function 'os_ro_anonymous_file_put_fd':
../weston-8.0.0/shared/os-compatibility.c:391:24: error: 'F_GET_SEALS' undeclared (first use in this function)
../weston-8.0.0/shared/os-compatibility.c:400:31: error: 'F_SEAL_WRITE' undeclared (first use in this function)

I think there is some more #ifdef HAVE_MEMFD_CREATE is missing. But I don't know what needs to be done when it's not available. @swick, you wrote that code. What needs to be done here?