Fix the following build warning by moving the 'seals' declaration inside the
HAVE_MEMFD_CREATE guard:
../shared/os-compatibility.c: In function ‘os_ro_anonymous_file_get_fd’:
../shared/os-compatibility.c:341:6: warning: unused variable ‘seals’ [-Wunused-variable]
int seals, fd;
^
Signed-off-by: Frank Binns <frank.binns@imgtec.com>