NSS: Replace exported NSS lookup functions with stubs [BZ #21962]

Commit 384ca55174 from 2007 added this to
nss/XXX-lookup.c:

+#ifndef NO_COMPAT
+int
+internal_function attribute_compat_text_section
+DB_COMPAT_FCT (service_user **ni, const char *fct_name, void **fctp)
+{
+  return DB_LOOKUP_FCT (ni, fct_name, NULL, fctp);
+}
+#endif

That is, it adds a pseudo-compat function with an internal_function
attribute.  The function it was supposed to replace did not have the
attribute:

 extern int DB_LOOKUP_FCT (service_user **ni, const char *fct_name,
-			  void **fctp) internal_function;
+			  const char *fct2_name, void **fctp)
+  internal_function;

This changed the calling convention on i386 for the following
functions in the public ABI:

  __nss_passwd_lookup
  __nss_group_lookup
  __nss_hosts_lookup

This commit replaces the functions with always-failing stubs,
with true compat symbols.  Due to a happy accident, the calling
convention of the stub is identical for the internal_function
and non-internal_function case on i386.

In addition, this commit auto-generates the __nss_*_lookup2
function declarations as part of <nsswitch.h>.

inet/ether_hton.c

@@ -27,11 +27,6 @@
 typedef int (*lookup_function) (const char *, struct etherent *, char *, int,
 				int *);
 
-/* The lookup function for the first entry of this service.  */
-extern int __nss_ethers_lookup (service_user **nip, const char *name,
-				void **fctp) internal_function;
-
-
 int
 ether_hostton (const char *hostname, struct ether_addr *addr)
 {
@@ -49,7 +44,7 @@ ether_hostton (const char *hostname, struct ether_addr *addr)
 
   if (startp == NULL)
     {
-      no_more = __nss_ethers_lookup (&nip, "gethostton_r", &fct.ptr);
+      no_more = __nss_ethers_lookup2 (&nip, "gethostton_r", NULL, &fct.ptr);
       if (no_more)
 	startp = (service_user *) -1;
       else