Index: Mk/Uses/compiler.mk
===================================================================
--- Mk/Uses/compiler.mk	(revision 462044)
+++ Mk/Uses/compiler.mk	(working copy)
@@ -95,11 +95,27 @@
 CHOSEN_COMPILER_TYPE=	${COMPILER_TYPE}
 
 .if ${_COMPILER_ARGS:Mopenmp}
-.if ${COMPILER_TYPE} == clang
-USE_GCC=	yes
+.if ${COMPILER_TYPE} == clang && ${ARCH} == amd64
+_USES_POST+=	localbase:ldflags
+BUILD_DEPENDS+=	llvm50>=0:devel/llvm50
+RUN_DEPENDS+=	llvm50>=0:devel/llvm50
+CPP=	${LOCALBASE}/bin/clang-cpp50
+CC=	${LOCALBASE}/bin/clang50
+CXX=	${LOCALBASE}/bin/clang++50
+CHOSEN_COMPILER_TYPE=	clang
+.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
 
 .if ${_COMPILER_ARGS:Mnestedfct}
 .if ${COMPILER_TYPE} == clang
Index: math/openblas/Makefile
===================================================================
--- math/openblas/Makefile	(revision 462044)
+++ math/openblas/Makefile	(working copy)
@@ -78,6 +78,8 @@
 .endif
 
 .if ${PORT_OPTIONS:MOPENMP}
+# due to the Fortran dependency, we must require USE_GCC here to avoid mixing different OpenMPs for Fortran and C/C++
+USE_GCC=	yes
 USES+=		compiler:openmp
 BUILDFLAGS_THREAD+=	USE_OPENMP=1
 .endif