6648 illumos build should be explicit about C standards

*** 1225,1235 ****
  # assym.h build rules
  
  GENASSYM_C = genassym.c
  
  genassym: $(GENASSYM_C)
!         $(NATIVECC) -Iinc -I$(LIBCDIR)/inc $(CPPFLAGS.native)   \
                  -o $@ $(GENASSYM_C)
  
  OFFSETS = $(LIBCDIR)/$(MACH)/offsets.in
  
  assym.h: $(OFFSETS) genassym
--- 1225,1235 ----
  # assym.h build rules
  
  GENASSYM_C = genassym.c
  
  genassym: $(GENASSYM_C)
!         $(NATIVECC) $(NATIVE_CFLAGS) -Iinc -I$(LIBCDIR)/inc $(CPPFLAGS.native) \
                  -o $@ $(GENASSYM_C)
  
  OFFSETS = $(LIBCDIR)/$(MACH)/offsets.in
  
  assym.h: $(OFFSETS) genassym