openssh: fix build w/ gcc-9.1.0

Signed-off-by: Jürgen Buchmüller <pullmoll@t-online.de>

srcpkgs/openssh/patches/auth2-pubkey_c-command.patch

@@ -0,0 +1,10 @@
+--- auth2-pubkey.c	2019-05-14 12:41:42.185855228 +0200
++++ auth2-pubkey.c	2019-05-14 12:44:49.649864899 +0200
+@@ -446,6 +446,7 @@
+ 		    username, strerror(errno));
+ 		goto out;
+ 	}
++	command = strdup(options.authorized_principals_command);
+ 
+ 	/* Turn the command into an argument vector */
+ 	if (argv_split(options.authorized_principals_command, &ac, &av) != 0) {