lang/gcc9-devel: Deprecate port

The purpose of lang/gcc9-devel and other lang/gcc*-devel ports
was to track GCC's weekly snapshots, serve as a canary for the
next update of the corresponding lang/gcc* port that tracks minor
releases, and provide bleeding edge for users who desire so.

Since I relinquished maintainership more than five months ago
(commit 11a4465) there has not
been an update and the port is stuck at the 20211007 snapshot.

It thus has not been serving its purpose any longer for a while
and GCC 9 is reaching end of life, so deprecate the port for
removal more than half a year after the latest version update.

lang/gcc9-devel/Makefile

@@ -2,6 +2,7 @@
 
 PORTNAME=	gcc
 PORTVERSION=	9.4.1.s20211007
+PORTREVISION=	1
 CATEGORIES=	lang
 MASTER_SITES=	GCC/snapshots/${DIST_VERSION}
 PKGNAMESUFFIX=	${SUFFIX}-devel
@@ -13,6 +14,8 @@ COMMENT=	GNU Compiler Collection 9
 LICENSE=	GPLv3 GPLv3RLE
 LICENSE_COMB=	multi
 
+DEPRECATED=	Not serving its purpose any longer due to lack of maintenance
+EXPIRATION_DATE=2022-04-14
 ONLY_FOR_ARCHS=	aarch64 amd64 arm armv6 armv7 i386 powerpc powerpc64 powerpc64le sparc64
 
 LIB_DEPENDS=	libgmp.so:math/gmp \