Build emscripten-snapshot-compiler without patching jerryscript

[mikee47]

This PR separates the snapshot compiler build from jerryscript by using pre-compiled libraries.

todo:

• Generated code is slightly different to previously - there's an additional invoke_viii function in there but not sure why... Works fine though, leave it.
• Add pre-compiled JSC for minimal/esnext profiles for application use (update Advanced sample accordingly)

[mikee47]

@slaff I've also removed the appveyor.yml from this because we can provide a generic script in the Sming repo. I'll have a separate PR for that.

[slaff]

@mikee47 Ready with this PR?

[mikee47]

@slaff Yep, all done.

[slaff]

Can you remove this file? I guess it was not meant to be part of this PR.

[mikee47]

@slaff I've got a version working with the current jerryscript master branch... See https://github.com/mikee47/Sming-jerryscript/tree/update/jerryscript-master

[slaff]

@mikee47 Ok, we can merge these changes in the develop branch of Sming-jerryscript librabry. Is there improvement in speed, memory usage, snapshot size ?

[mikee47]

Generated sizes are similar and samples work correctly. I haven't done any speed tests but don't expect that to change. There are a lot of fixes and improvements but signficantly the API has changed. That means any work we do now should be compatible with the next release rather than having to apply it retrospectively.