Autoconf doesn't use them either.
Thanks to Jirka Kubias for reporting this.
$(CPPFLAGS) $(OMK_CFLAGS) $(CFLAGS) -DOMK_FOR_USER
cc_o_COMPILE = $(CXX) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(OMK_CPPFLAGS) \
- $(CPPFLAGS) $(OMK_CFLAGS) $(CFLAGS) $(OMK_CXXFLAGS) $(CXXFLAGS) -DOMK_FOR_USER
+ $(CPPFLAGS) $(OMK_CXXFLAGS) $(CXXFLAGS) -DOMK_FOR_USER
S_o_COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(OMK_CPPFLAGS) \
$(CPPFLAGS) $(OMK_CFLAGS) $(CFLAGS) $(ASFLAGS) -DOMK_FOR_USER