Shared library support: Where we are at

[rikki cattermole]

Wahoooooo joy to the world we have another bug report that could be 
closed by getting exportation of ModuleInfo fixed.

https://issues.dlang.org/show_bug.cgi?id=6019

Current running total is four if this one issue were to be solved 
satisfactorily.

https://issues.dlang.org/show_bug.cgi?id=22367
https://issues.dlang.org/show_bug.cgi?id=9816
https://issues.dlang.org/show_bug.cgi?id=4071

This is a set of very high value set of bug reports that could be fixed 
very easily if someone with knowledge of dmd compiler internals wanted 
to fix it.

See: https://forum.dlang.org/post/ohflhdaggtapeqpynkjd@forum.dlang.org

Latest attempt of mine to fix this: https://github.com/dlang/dmd/pull/14647