Add nopshufb tag

[klauspost]

Add nopshufb tag that should remove all code utilizing PSHUFB - and similar code on other platforms.

Background

None of section below is legal advice. Seek your own legal counsel.
As stated by the LICENSE the authors will not be held reliable for any use of this library.
Users are encouraged to independently verify they comply with all legal requirements.

As can be seen in recent news there has been lawsuits related to possible patents of aspects of erasure coding functionality.

As a possible mitigation it is possible to use the tag nopshufb when compiling any code which includes this package.
This will remove all inclusion and use of PSHUFB and equivalent on other platforms.

This is done by adding -tags=nopshufb to go build and similar commands that produce binary output.

The removed code may not be infringing and even after -tags=nopshufb there may still be infringing code left.