6648 illumos build should be explicit about C standards

*** 1298,1308 ****
  assym.h := CFLAGS64 += -g
  
  GENASSYM_C = $(LIBCDIR)/$(MACH)/genassym.c
  
  genassym: $(GENASSYM_C)
!         $(NATIVECC) -I$(LIBCBASE)/inc -I$(LIBCDIR)/inc \
                  $(CPPFLAGS.native) -o $@ $(GENASSYM_C)
  
  OFFSETS = $(LIBCDIR)/$(MACH)/offsets.in
  
  assym.h: $(OFFSETS) genassym
--- 1298,1308 ----
  assym.h := CFLAGS64 += -g
  
  GENASSYM_C = $(LIBCDIR)/$(MACH)/genassym.c
  
  genassym: $(GENASSYM_C)
!         $(NATIVECC) $(NATIVE_CFLAGS) -I$(LIBCBASE)/inc -I$(LIBCDIR)/inc \
                  $(CPPFLAGS.native) -o $@ $(GENASSYM_C)
  
  OFFSETS = $(LIBCDIR)/$(MACH)/offsets.in
  
  assym.h: $(OFFSETS) genassym