deve/gdb: ignore instead of disconnecting

Mark the port as ignored instead of disconnecting it from the ports
build system. This way a user trying to explicitly build this port will
be informed that it's ignored on CheriBSD.

devel/Makefile

@@ -741,14 +741,7 @@
     SUBDIR += gcli
     SUBDIR += gconf2
     SUBDIR += gconfmm26
-#
-# devel/gdb is replaced by devel/gdb-meta that points at devel/gdb-cheri on
-# CheriBSD.
-#
-# Do not build devel/gdb but leave it in CheriBSD ports to prevent possible
-# upstream merge issues.
-#
-#    SUBDIR += gdb
+    SUBDIR += gdb
     SUBDIR += gdb-cheri
     SUBDIR += gdb-meta
     SUBDIR += gdcm

devel/gdb/Makefile

@@ -1,4 +1,6 @@
 .ifndef SLAVE_PORT
+IGNORE=		is replaced by devel/gdb-meta on CheriBSD
+
 PORTNAME=	gdb
 DISTVERSION=	13.1
 PORTREVISION=	3