Copy public zstd_errors.h into output directory (#68)
Copy public zstd_errors.h into output directory (#68)

The common/zstd_errors.h header file is also part of the public
interface of the zstd library. Copy it into the output directory, [like
the upstream build system does][0], so that downstream dependencies can
find it.

[0]: https://github.com/facebook/zstd/blob/0f9866add2df8e824c96f67fc49a7d5b69ad3317/lib/Makefile#L275
Gyscos/zstd-rs,Gyscos/zstd-rs