Index: Mk/Uses/compiler.mk
===================================================================
--- Mk/Uses/compiler.mk
+++ Mk/Uses/compiler.mk
@@ -96,8 +96,25 @@
 
 .if ${_COMPILER_ARGS:Mopenmp}
 .if ${COMPILER_TYPE} == clang
-USE_GCC=	yes
+.if ${ARCH} == amd64
+_USES_POST+=	localbase:ldflags
+.if ${COMPILER_VERSION} < 38
+CFLAGS+=	-D_OPENMP
+.endif
+LIB_DEPENDS+=	libomp.so.0:devel/openmp
+LDFLAGS+=	-lomp
+.else
+USE_GCC=		yes
 CHOSEN_COMPILER_TYPE=	gcc
+.if ${COMPILER_FEATURES:Mlibc++}
+CXXFLAGS+=	-nostdinc++ -isystem /usr/include/c++/v1
+LDFLAGS+=	-L${WRKDIR}
+
+_USES_configure+=	200:gcc-libc++-configure
+gcc-libc++-configure:
+	@${LN} -fs /usr/lib/libc++.so ${WRKDIR}/libstdc++.so
+.endif
+.endif
 .endif
 .endif
 
Index: math/openblas/Makefile
===================================================================
--- math/openblas/Makefile
+++ math/openblas/Makefile
@@ -73,6 +73,7 @@
 .endif
 
 .if ${PORT_OPTIONS:MOPENMP}
+USE_GCC=	yes
 USES+=		compiler:openmp
 BUILDFLAGS_THREAD+=	USE_OPENMP=1
 .endif