Name (de)mangling for C++20 modules

[Jones, Andrew via Gcc]

Reading over 
https://gcc.gnu.org/wiki/cxx-modules?action=AttachFile&do=view&target=module-abi-2017-09-01.pdf,
 in particular Section 4 ("Recommendation"), it suggests that code such as:

```
export module moo;

int moo() { return 10; }

```

should "have module-linkage include the module name in their mangling", and 
indeed it appears this is the case:

```
0000000000000000 g     F .text  000000000000000b _ZW3mooE3moov

```

(from objdump @ 75f03fa7743, compiled with GCC 11.0.0).

However, I have two questions:

    1) What should the demanging (e.g., via c++filt) of `_ZW3mooE3moov` be?

    2) How should the presentation of demangling `_ZW3mooE3moov` (in the module 
case) differ from the demangling of `_ZN3moo3mooEv` (in the case where you have 
a method `moo` in a namespace `moo`)?

Cheers,

Andrew