6648 illumos build should be explicit about C standards

@@ -21,17 +21,23 @@
 
 ASSUFFIX_sparc  = S
 ASSUFFIX_i386   = s
 ASSUFFIX        = $(ASSUFFIX_$(MACH))
 
-# C99MODE of neither enabled nor disabled is "no_lib", whereby we expect
-# C99-the-language, but don't modify the behaviour of library routines.  This
-# is VERY IMPORTANT, as -xc99=%all, for instance, would link us with
+# With studio C99MODE of neither enabled nor disabled is "no_lib", whereby we
+# expect C99-the-language, but don't modify the behaviour of library routines.
+# This is VERY IMPORTANT, as -xc99=%all, for instance, would link us with
 # values-xpg6, which would introduce an __xpg6 to our object with the C99
 # flags set, causing us to default C99 libm behaviour on, breaking
 # compatibility.
+#
+# We must then, unfortunately, defeat the GNU compiler _defaulting_ to C99, by
+# in that case setting it back to gnu89, which _also_ accepts C99 syntax as
+# far as is important.
 C99MODE         =
+CFLAGS          += -_gcc=-std=gnu89
+CFLAGS64        += -_gcc=-std=gnu89
 
 M4FLAGS         = -D__STDC__ -DPIC
 
 LDBLDIR_sparc   = Q
 LDBLDIR_i386    = LD

@@ -47,11 +53,11 @@
                 -I$(LIBMSRC)/$(LDBLDIR) -I$(LIBMDIR)/$(TARGET_ARCH)/src
 
 # GCC needs __C99FEATURES__ such that the implementations of isunordered,
 # isgreaterequal, islessequal, etc, exist.  This is basically equivalent to
 # providing no -xc99 to Studio, in that it gets us the C99 language features,
-# but not values-xpg6, the reason for which is outline with C99MODE.
+# but not values-xpg6, the reason for which is outlined with C99MODE.
 CFLAGS          += -_gcc=-D__C99FEATURES__
 CFLAGS64        += -_gcc=-D__C99FEATURES__
 
 # libm depends on integer overflow characteristics
 CFLAGS          += -_gcc=-fno-strict-overflow