Determine CONDA_ENV_SYSROOT from environment

[pearu]

Checklist

• Used a fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

See discussions in:
https://github.com/conda-forge/staged-recipes/pull/9225/files#r330386001

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[pearu]

@conda-forge-admin, please rerender

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-webservice.

I tried to re-render for you, but it looks like there was nothing to do.

[kkraus14]

@jakirkham I think you should review this as I know you had opinions regarding how we detect the sysroot.

[jakirkham]

Thanks for the work here. Sorry for the delay. Am a bit slammed ATM. So likely won't have time to look until some time midweek next week. Sorry again for the delay.

[pearu]

The recent gcc_linux-64 provides CONDA_BUILD_SYSROOT (PR conda-forge/ctng-compiler-activation-feedstock#9), so we don't need to determine CONDA_ENV_SYSROOT in the nvcc installation script anymore.

@isuruf @jakirkham , please review.

[kkraus14]

Changes look good to me, but would defer to @jakirkham here as he had the most opinions about the sysroot

[jakirkham]

I think now with PR ( conda-forge/ctng-compiler-activation-feedstock#9 ) in and the updates here, this LGTM.

[jakirkham]

Thanks @pearu! 😄