cad/openvsp: fix build without libomp

CMake Error at /usr/local/share/cmake/Modules/FindOpenMP.cmake:261 (try_compile):
  Failed to generate test project build system.
Call Stack (most recent call first):
  /usr/local/share/cmake/Modules/FindOpenMP.cmake:537 (_OPENMP_GET_FLAGS)
  src/vsp_aero/Solver/CMakeLists.txt:9 (FIND_PACKAGE)

-fpermissive necessary because of:
/usr/include/c++/v1/__memory/compressed_pair.h:48:9: error: invalid conversion from 'int' to 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >*' [-fpermissive]

cad/openvsp/Makefile

@@ -24,8 +24,14 @@ LIB_DEPENDS=	libdrm.so:graphics/libdrm \
 		libfltk.so:x11-toolkits/fltk \
 		libcpptest.so:devel/cpptest
 
-USES=		compiler:c++11-lang cmake:noninja localbase\
+USES=		cmake:noninja localbase\
 		gl gnome jpeg xorg
+.if !exists(/usr/include/omp.h)
+CXXFLAGS+=	-fpermissive
+USES+=		compiler:gcc-c++11-lib
+.else
+USES+=		compiler:c++11-lang 
+.endif
 USE_GITHUB=	yes
 GH_ACCOUNT=	${GH_PROJECT}
 GH_PROJECT=	OpenVSP