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 complex4;

void main()
{
    cfloat c = 2f + 3fi;
    float r = cast(float)c;
    ifloat i = cast(ifloat)c;
}