Put pointers to ModuleInfo into dminfo section
Rebuild d-confdefs.h if target-ver-syms.sh changes
Link against __sharedlib.o

* when linking a shared library with gdc -shared
* when linking the application
but only on linux for now.

__sharedlib.o is searched for by the startfile spec, which means that
it must be in a directory specified via -B options. Once GDC is
installed correctly it'll always find the file, but as long
as it's not installed (testsuite) the path must be specified
via -B flags.
Update testsuite runner for shared library support
Build system changes for shared libraries
Implement shared library support in druntime