cpp: enable as many warnings as practical

*** 31,41 ****
          y.tab.o$(STRAP)
  
  CLEANFILES += \
          y.tab.c$(STRAP)
  
! CFLAGS +=       -O2
  LD =            $(GCC)
  
  COMPILE.c =     $(GCC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@
  LINK.prog =     $(LD) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
  PROTOFILES =    $(DESTDIR)$(PROGDIR)/$(PROG)
--- 31,45 ----
          y.tab.o$(STRAP)
  
  CLEANFILES += \
          y.tab.c$(STRAP)
  
! CERRWARN=       -Wall -Wextra
! CERRWARN +=     -Wno-unknown-pragmas
! CERRWARN +=     -Wno-sign-compare
! CERRWARN +=     -Wno-unused-label
! CFLAGS +=       -O2 $(CERRWARN)
  LD =            $(GCC)
  
  COMPILE.c =     $(GCC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@
  LINK.prog =     $(LD) $(LDFLAGS) -o $@ $(OBJS) $(LIBS)
  PROTOFILES =    $(DESTDIR)$(PROGDIR)/$(PROG)