DW_TAG_module experiment.

[Iain Buclaw]

Hi all,

This weeks experiment is with actually building a NAMESPACE_DECL 
for D modules, and emitting them as DW_TAG_module in dwarf2out.c


https://github.com/D-Programming-GDC/GDC/commit/91a1863170431a37de473011c148f4927a2a3944


After some thought, I've decided it best not to set the 
NAMESPACE_DECL for symbols that are:

- Not declared with D linkage - !extern(D) symbols should be 
considered as part of the global namespace.
- Not D main.  This is important, as we don't want to break this 
fix in gdb: 
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=6377854769ea85f2dd38aac9a9b11fded61245f3


Johannes, I've only updated the 4.9.x patches. You may want to 
backport this after my gdb changes have been submitted and pushed 
into gdb-development (which will be the gdb-7.8 release).


Martin, not sure if you read these lists, but I am curious if you 
have don't something similar for DMD.

Regards,
Iain.