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 structs7;

struct S
{
    int i;
    long l;
}

void main()
{
    S s = void;
    int i = s.i;
    long l = s.l;
}