Mostly rewrite debug info generation in terms of llvm/Analysis/DebugInfo.h. Add getCompilationModule to Dsymbol and fix template compile unit decision code. Runtime compiles with -g again.

module bug74;

char[] sformat(char[] s, ...)
{
    TypeInfo[] ti = _arguments;
    void* args = _argptr;
    return "";
}

void main()
{
}