Update build falgs for 2.1.0

[t20100]

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.

This PR builds on PR #3 and updates the build options to:

• disable c++11 for Linux, macOS as there is an issue with macOS (Building with C++11 fails on macOS silx-kit/hdf5plugin#58). For Windows, it will be used for python3.
• tune build option to build for generic x86_64 cpus (i.e., no native, sse2 on, avx2 off, openmp off)
  closes Build flags for the next version of hdf5plugin #2

[t20100]

@conda-forge-admin, please rerender

[t20100]

This PR is using the same build number as PR #3... Is it an issue?

[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.

[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.

[tschoonj]

Looking good. Attached a commit that removes some extraneous lines in build.sh. Will merge in afterwards.

By the way would you like to be added as a maintainer?

[t20100]

Yes, you can add me as a maintainer.