Align swiftenv-build works with Swift 3.x

[sinoru]

This make swiftenv-build using self-defined presets that almost same as swift linux build one.

[sinoru]

Testing:

• 2.2.1 on macOS
• 3.0.1 on macOS
• 2.2.1 on Ubuntu 16.04
• 3.0.1 on Ubuntu 16.04

[sinoru]

Build Re-Testing after 3b061fb

• 2.3-dev on macOS
• 3.0.1 on macOS (REPL doesn't work. I thinks this due to lldb codesign)
• 2.2.1 on Ubuntu 16.04
• 3.0.1 on Ubuntu 16.04

[sinoru]

All works!

[sinoru]

All CI tests passed!

[fcrespo82]

Is there a timeframe to merge this?
Can I help in anyway?
Would be of much help for the plugin I made (asdf-swift) for asdf that depends on it.

[kylef]

Thanks for this @sinoru. I'm sorry I have not got round to looking at this PR yet. Testing this out is going to be a little tricky as I do not have much hardware that is capable of building Swift in a reasonable time. I am wondering how we could automate testing on various platforms.

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There is a lot of complexity here and I think it would be great if Swift could provide a single tarball including the source of all versions. I've tried to open a discussion on the Swift evolution list that can be found at https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161212/029433.html .

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Can I help in anyway?

@fcrespo82 Yes, you could help test on as many platforms as you can and report back your experiences.

[sinoru]

@kylef You're right. It is hard to test it. Even I try on Travis CI, this leads timeout.
Uhm... I have some idle linux VPS servers.. that I can offer jenkins to test it maybe?
But, Still... building swift on Swift Projects' own CI(jenkins) takes almost 1 hour that is too long to test it frequently.

So until swift has own idea to handle well to build it, maybe we can flag this feature as experimental.

[sinoru]

Rebased on latest #73.