ASM library

[lrytz]

ASM library.

Source code is taken from https://github.com/scala/scala/tree/master/src/asm, the package name is changed from scala.tools.asm to dotty.tools.asm.

The commits reflect the evolution of the ASM source code in scala/scala.

Review by @magarciaEPFL

[adriaanm]

I would suggest considering the approach we're planning to implement in Scala 2.12. It'll be some variation on https://github.com/adriaanm/scala/compare/asm5.

[adriaanm]

One downside (and a reason I didn't push for it) is that the shading as implemented there rewrites the whole scala-compiler jar (so that we don't have a separate asm jar). I think it would be better to have a scala-asm artifact that the compiler can depend on explicitly.

[lrytz]

Right, I thought about the other options. I think doing the same thing as scalac simplifies things. It will be easy to port any changes over to dotc.

[magarciaEPFL]

@lrytz why not merge this PR into the backend branch first, as we've been doing so far? Doing so will later allow us to distill a cleaner history for merging into master. Other than that, looks good.

[lrytz]

OK for me, I'll create a new PR then