Added specified nightly toolchain support

[sprhawk]

1. build-new-version.sh: added support to download specified nightly version
2. fix cargo-bin-cross.inc and rust-bin-cross.inc to support nightly version
3. added nightly 2019-07-08 version recipe ( optee requires specified nightly version )

Question: How can I specify a toolchain only to certain recipe? PREFERRED_VERSION only support selection of toolchain globally.

[nindoja]

Definitely interested in getting this pulled in since some nightly features would be great to have in a yocto recipe.

[sprhawk]

Definitely interested in getting this pulled in since some nightly features would be great to have in a yocto recipe.

you can try it by using my own repo

[posborne]

With comments addressed, I think it is reasonable to include the script changes to support nightly and documentation in tree. To avoid having a consistently out of date nightly in tree, however, I think we should just set the expectation that if you want to use a nightly rust version in your layer that you'll need to generate the recipe using the script and maintain the generated bit outside of this tree. Most likely systems using a nightly compiler will be bumping versions regularly until required features are stable anyhow.

[sprhawk]

Agree, I just want to use that nightly version as an example there. I will remove then.

[nindoja]

@posborne any updates on getting this merged in?

[posborne]

Sorry for the long delay and thanks for making these update to the script @sprhawk