[v2.28] Build a variant without features to use latest sysroot outside conda-build

[h-vetinari]

Backport #88 (itself a rebase of #75)

[conda-forge-admin]

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/meta.yaml) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe/meta.yaml:

• ℹ️ The recipe is not parsable by parser conda-souschef (grayskull). This parser is not currently used by conda-forge, but may be in the future. We are collecting information to see which recipes are compatible with grayskull.
• ℹ️ License exception is not an SPDX exception.

Documentation on acceptable licenses can be found here.

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