Add a --enable-opt compile-time switch

configure.ac

@@ -135,6 +135,14 @@ AC_ARG_ENABLE(debug,
   ])
 ])
 
+AC_ARG_ENABLE(opt,
+[AS_HELP_STRING(--enable-opt,Optimize for the native CPU - The resulting library will be faster but not portable)],
+[
+  AS_IF([test "x$enableval" = "xyes"], [
+    CFLAGS="$CFLAGS -flto -march=native"
+    LDFLAGS="$LDFLAGS -flto -march=native"])
+])
+
 AC_SUBST([MAINT])
 
 dnl Checks