devel/llvm-{cheri,morello}: future-proof ABI arguments

-Xclang arguments may become unused with never compiler versions so
bracket them with --start-no-unused-arguments/--end-no-unused-arguments
to silence warnings.

Reported by:	jrtc27
Sponsored by:	DARPA, AFRL

devel/llvm-cheri/Makefile

 PORTNAME=	llvm
 PORTVERSION=	${LLVM_MAJOR}.0.d${SNAPDATE}
-PORTREVISION=	2
+PORTREVISION=	3
 CATEGORIES=	devel lang
 PKGNAMESUFFIX=	${LLVM_SUFFIX}
 

devel/llvm-cheri/files/wrapper-cheri.sh.in

@@ -160,7 +160,7 @@ if [ $CHERIBSD_VERSION -gt 0 ]; then
 				vararg_flags="-Xclang -morello-vararg=new -Xclang -morello-bounded-memargs"
 			fi
 
-			arch_cflags="-march=morello -mabi=purecap $tls_flags $vararg_flags"
+			arch_cflags="-march=morello -mabi=purecap --start-no-unused-arguments $tls_flags $vararg_flags --end-no-unused-arguments"
 			arch_objdump_flags="--mattr=+morello"
 		else
 			vararg_flags=