biology/cd-hit: allow to build without GCC on libomp-less systems

biology/cd-hit/Makefile

 PORTNAME=		cd-hit
 DISTVERSIONPREFIX=	V
 DISTVERSION=		4.8.1
-PORTREVISION=		2
+PORTREVISION=		3
 CATEGORIES=		biology
 
 MAINTAINER=	jwb@FreeBSD.org
@@ -17,10 +17,10 @@ GH_ACCOUNT=	weizhongli
 GH_PROJECT=	cdhit
 SHEBANG_FILES=	${WRKSRC}/*.pl
 
+.if exists(/usr/include/omp.h)
 MAKE_FLAGS=	openmp=yes
-
-.if !exists(/usr/include/omp.h)
-USES+=		compiler:gcc-c++11-lib
+.else
+MAKE_FLAGS=	openmp=no
 .endif
 
 post-patch: