gcc12's regex header file relies on a std::vector<int> instance, export it.

The C++ modules marks the std::vector<int> instantiation as not visible because
it came from the `regex` header file which we did not explicitly include.

root-project/root@a785402 introduces checks if certain declaration is visible
in dictionary generation time which was intending to semantically improve the
coherence by what the user "allowed" (or requested) rootcling to see vs what
it can see globally. While this model works well it seems to not work for
template instantiations as they won't be re-instantiated with visible modifier.

This patch works around the current issue seen with libstdc++ 12 but a better
solution would be to implement a finer grained control over the implicit template
instatiations when generating a dictionary.

Fixes root-project/root#11329

include/cling/std.modulemap

@@ -273,6 +273,7 @@ module "std" [system] {
   }
   module "regex" {
     export *
+    export vector
     header "regex"
   }
   module "scoped_allocator" {