devel/flang-clang: Deprecate and set expiration date to 2022-09-30

Current version is very outdated and unsupported upstream
Upstream is working to improve Flang compiler included in LLVM

See https://github.com/flang-compiler/flang/wiki for more information

This change was also discussed with bapt

PR:		263810
Approved by:	jmd (maintainer timeout, 6+ weeks)

devel/flang-clang/Makefile

@@ -13,6 +13,9 @@ LICENSE_NAME=	LLVM Release License
 LICENSE_FILE=	${WRKSRC}/LICENSE.TXT
 LICENSE_PERMS=	dist-mirror dist-sell pkg-mirror pkg-sell auto-accept
 
+DEPRECATED=	Very outdated and unsupported upstream, current version in tree is several years old and upstream is still active
+EXPIRATION_DATE=2022-09-30
+
 ONLY_FOR_ARCHS=	amd64
 
 LLVM_VER=	70