cad/horizon-eda: Add back the workaround for clang crash that was mistakenly removed earlier

Reported by:	fallout

cad/horizon-eda/Makefile

 PORTNAME=	horizon-eda
 DISTVERSIONPREFIX=	v
 DISTVERSION=	2.1.0
+PORTREVISION=	1
 CATEGORIES=	cad
 
 MAINTAINER=	yuri@FreeBSD.org
@@ -34,6 +35,12 @@ BINARY_ALIAS=	python3=${PYTHON_CMD}
 
 INSTALLS_ICONS=	yes
 
+LLVM_VER=	10 # workaround for bug#253551
+BUILD_DEPENDS+=	clang${LLVM_VER}:devel/llvm${LLVM_VER}
+CPP=		clang-cpp${LLVM_VER}
+CC=		clang${LLVM_VER}
+CXX=		clang++${LLVM_VER}
+
 post-install: # https://github.com/horizon-eda/horizon/issues/558
 	cd ${STAGEDIR}${PREFIX}/bin && ${STRIP_CMD} horizon-eda