Change regex! macro to expand to a constexpr, allowing to put it in a static

src/libregex/lib.rs

@@ -401,7 +401,7 @@ pub mod native {
     // undesirable consequences (such as requiring a dependency on
     // `libsyntax`).
     //
-    // Secondly, the code generated generated by `regex!` must *also* be able
+    // Secondly, the code generated by `regex!` must *also* be able
     // to access various functions in this crate to reduce code duplication
     // and to provide a value with precisely the same `Regex` type in this
     // crate. This, AFAIK, is impossible to mitigate.