I played around with:
`@if test "$(suffix $<)" = ".c"; then \
        $(CC) $(CFLAGS) $(INCLUDES) -c $< -o $(BINDIR)$(PROJECT)/$*.o; \
    fi;
ifeq ($(CPPMIX),1)
    @if test "$(suffix $<)" = ".cpp"; then \
        $(CPPMIXCC) $(CPPMIXCFLAGS) $(INCLUDES) -c $< -o $(BINDIR)$(PROJECT)/$*.o; \
    fi;
endif`
But I found the alternative #981 from @dangnhat using Makfile rules to distinguish source files more reasonable. ( So I just stole them ;) )