glr2.cc: avoid warnings about long long

* data/skeletons/glr2.cc: Disable the warning before triggering it.

TODO

@@ -151,8 +151,35 @@ Line -1 and -3 should mention CATEGORIE, not CATEGORY.
 
 * Bison 3.8
 ** Rewrite glr.cc
+*** glr.c
 Get rid of scaffolding in glr.c.
 
+*** pragmas in glr2.cc
+Remove the pragmas that disable some warnings:
+
+    // This skeleton is based on C, yet compiles it as C++.
+    // So expect warnings about C style casts.
+    #if defined __clang__ && 306 <= __clang_major__ * 100 + __clang_minor__
+    # pragma clang diagnostic ignored "-Wold-style-cast"
+    #elif defined __GNUC__ && 406 <= __GNUC__ * 100 + __GNUC_MINOR__
+    # pragma GCC diagnostic ignored "-Wold-style-cast"
+    #endif
+
+    // On MacOS, PTRDIFF_MAX is defined as long long, which Clang's
+    // -pedantic reports as being a C++11 extension.
+    #if defined __APPLE__ && YY_CPLUSPLUS < 201103L \
+        && defined __clang__ && 4 <= __clang_major__
+    # pragma clang diagnostic ignored "-Wc++11-long-long"
+    #endif
+
+We should use clean C++ code.
+
+*** namespaces in glr2.cc
+StrongIndexAlias should be in the parser's namespace.  Possibly even an
+inner class.
+
+
+* Chains
 ** Unit rules / Injection rules (Akim Demaille)
 Maybe we could expand unit rules (or "injections", see
 https://homepages.cwi.nl/~daybuild/daily-books/syntax/2-sdf/sdf.html), i.e.,