Fix (most of) compilation warnings

[daneos]

Attempt to clean up warnings.

Warnings still left to clean up:

  ../nfs_utils.c:118:5: warning: implicit declaration of function ‘iocshSetError’ [-Wimplicit-function-declaration]
    118 |     iocshSetError(save_restoreSet_NFSHost(args[0].sval, args[1].sval, args[2].sval));
        |     ^~~~~~~~~~~~~

Happens only with base 3.15, where iocshSetError doesn't seem to exist. I'm not entirely sure why it doesn't fail the build instead.

  ../save_restore.c: In function ‘concatenate_paths’:
  ../save_restore.c:754:9: warning: ‘__builtin_strncat’ output may be truncated copying between 0 and 254 bytes from a string of length 254 [-Wstringop-truncation]
    754 |         strncat(dest, &(tmp2[1]), MAX(MAX_PATH_LEN - 1 - strlen(dest), 0));
        |         ^
  ../save_restore.c:756:9: warning: ‘__builtin_strncat’ output may be truncated copying between 0 and 254 bytes from a string of length 254 [-Wstringop-truncation]
    756 |         strncat(dest, tmp2, MAX(MAX_PATH_LEN - 1 - strlen(dest), 0));
        |         ^

Fixing this would require either some heavy-ish refactoring of concatenate_paths or providing it with the size of dest buffer.