6648 illumos build should be explicit about C standards

*** 24,35 ****
  CMD32 = $(PROG:%=$(TESTDIR)/%.$(MACH))
  CMD64 = $(PROG:%=$(TESTDIR)/%.$(MACH64))
  CMDS = $(CMD32) $(CMD64)
  $(CMDS) := FILEMODE = 0555
  
! C99MODE = -xc99=%all
! CFLAGS = -I $(SRC)/uts/common -D_KERNEL
  LDLIBS += -lmd
  LINTFLAGS += -u
  LINTFLAGS64 += -u
  
  all: $(PROG) $(TESTDIR)
--- 24,35 ----
  CMD32 = $(PROG:%=$(TESTDIR)/%.$(MACH))
  CMD64 = $(PROG:%=$(TESTDIR)/%.$(MACH64))
  CMDS = $(CMD32) $(CMD64)
  $(CMDS) := FILEMODE = 0555
  
! C99MODE = $(C99_ENABLE)
! CFLAGS += -I $(SRC)/uts/common -D_KERNEL
  LDLIBS += -lmd
  LINTFLAGS += -u
  LINTFLAGS64 += -u
  
  all: $(PROG) $(TESTDIR)