[OF6] exit if cfdemSolverMultiphase is compiled against OF6

cfdemSolverMultiphase malfunctions in combination with OpenFOAM 6.
The root of this erroneous behaviour remains unclear at this point.

applications/solvers/cfdemSolverMultiphase/Make/options

@@ -1,6 +1,10 @@
+FOAM_VERSION_MAJOR := $(word 1,$(subst ., ,$(WM_PROJECT_VERSION)))
+PFLAGS+= -DOPENFOAM_VERSION_MAJOR=$(FOAM_VERSION_MAJOR)
+
 include $(CFDEM_ADD_LIBS_DIR)/additionalLibs
 
 EXE_INC = \
+     $(PFLAGS) \
     -I$(CFDEM_OFVERSION_DIR) \
     -ImultiphaseMixture/lnInclude \
     -I$(LIB_SRC)/transportModels \

applications/solvers/cfdemSolverMultiphase/cfdemSolverMultiphase.C

@@ -46,6 +46,11 @@ Description
 
 int main(int argc, char *argv[])
 {
+
+#if OPENFOAM_VERSION_MAJOR >= 6
+    FatalError << "cfdemSolverMultiphase requires OpenFOAM 4.x or 5.x to work properly" << exit(FatalError);
+#endif
+
     #include "postProcess.H"
     #include "setRootCase.H"
     #include "createTime.H"