added configure option for enabling march=native gcc 4.2 and later

configure.in

@@ -169,6 +169,25 @@ AC_INIT(configure.in)
     CFLAGS="${CFLAGS} -pg"
     fi
 
+#enable gcc march=native gcc 4.2 or later
+    AC_ARG_ENABLE(gccmarch_native,
+            [  --enable-gccmarch-native Enable gcc march=native gcc 4.2 and later only],
+            [ enable_gccmarch_native=yes
+            ])
+
+    if test "$enable_gccmarch_native" = "yes"; then
+        if test "$gccvernum" -ge "402"; then
+                dnl gcc 4.2 or later
+                CFLAGS="$CFLAGS -march=native"
+        else
+                echo
+                echo "   You specified --enable-gccmarch-native but looks like you are running gcc < 4.2"
+                echo "   Please update your version of gcc or remove this option from configure."
+                echo
+                exit 1
+        fi
+    fi
+
 #libpcre
     AC_ARG_WITH(libpcre_includes,
             [  --with-libpcre-includes=DIR  libpcre include directory],