negTokenInit_t.mechtypes is defined as
  const char **mechTypes;
yet utils/ntlm_auth.c::offer_gss_spnego_mechs() initializes it with:
  spnego.negTokenInit.mechTypes = SMB_XMALLOC_ARRAY(char *, 3)
This causes a compile error when the appropriate gcc warnings are enabled
(c.f., "char *" instead of "const char *")

The fix is trivial; use
  spnego.negTokenInit.mechTypes = SMB_XMALLOC_ARRAY(const char *, 3);
instead.

I can provide a patch if necessary