On Mac, don't use -march=native by default unless using gcc >= 4.3.

configure.in

@@ -184,10 +184,22 @@ AC_INIT(configure.in)
     AC_ARG_ENABLE(gccmarch_native,
            AS_HELP_STRING([--enable-gccmarch-native], [Enable gcc march=native gcc 4.2 and later only]),,[enable_gccmarch_native=yes])
     AS_IF([test "x$enable_gccmarch_native" = "xyes"], [
+        case $host in
+	    *darwin*|*Darwin*)
+		if test "$gccvernum" -ge "403"; then
+                    dnl gcc 4.3 or later
+                    CFLAGS="$CFLAGS -march=native"
+		else
+		    enable_gccmarch_native=no
+		fi
+		;;
+	    *)
 		if test "$gccvernum" -ge "402"; then
                     dnl gcc 4.2 or later
                     CFLAGS="$CFLAGS -march=native"
 		fi
+		;;
+	esac
     ])
 
 #libpcre