nfsd: fix compile error

"fs/built-in.o: In function `supported_enctypes_show':
nfsctl.c:(.text+0x7beb0): undefined reference to `gss_mech_get_by_name'
nfsctl.c:(.text+0x7bebc): undefined reference to `gss_mech_put'
"
Reported-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsctl.c

@@ -189,6 +189,7 @@ static struct file_operations export_features_operations = {
 	.release	= single_release,
 };
 
+#ifdef CONFIG_SUNRPC_GSS
 static int supported_enctypes_show(struct seq_file *m, void *v)
 {
 	struct gss_api_mech *k5mech;
@@ -214,6 +215,7 @@ static struct file_operations supported_enctypes_ops = {
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
+#endif /* CONFIG_SUNRPC_GSS */
 
 extern int nfsd_pool_stats_open(struct inode *inode, struct file *file);
 extern int nfsd_pool_stats_release(struct inode *inode, struct file *file);
@@ -1425,7 +1427,9 @@ static int nfsd_fill_super(struct super_block * sb, void * data, int silent)
 		[NFSD_Versions] = {"versions", &transaction_ops, S_IWUSR|S_IRUSR},
 		[NFSD_Ports] = {"portlist", &transaction_ops, S_IWUSR|S_IRUGO},
 		[NFSD_MaxBlkSize] = {"max_block_size", &transaction_ops, S_IWUSR|S_IRUGO},
+#ifdef CONFIG_SUNRPC_GSS
 		[NFSD_SupportedEnctypes] = {"supported_krb5_enctypes", &supported_enctypes_ops, S_IRUGO},
+#endif /* CONFIG_SUNRPC_GSS */
 #ifdef CONFIG_NFSD_V4
 		[NFSD_Leasetime] = {"nfsv4leasetime", &transaction_ops, S_IWUSR|S_IRUSR},
 		[NFSD_Gracetime] = {"nfsv4gracetime", &transaction_ops, S_IWUSR|S_IRUSR},