Zstd: installation with MSYS2

[vtorri]

With MSYS2 + mingw-w64, we can install stuff as it's an emulation of a POSIX system (I did that for lz4)

mingw-w64 32 bits : uname returns :
MINGW32_NT-6.1-7601

mingw-w64 64 bits : uname returns :
MINGW64_NT-6.1-7601

[terrelln]

I don't have a MSYS2 system to test on, but if we want to support MSYS2 I see two things that we need:

1. We need a MSYS2 test in our appveyor CI. Otherwise it will bitrot and break.
2. We need to make installation work.

We're happy to accept PRs to that end.

[vtorri]

i'll work on this soon

[vtorri]

here is a first attempt. If it looks good, i can do a pull request this evening

mingw.zip

[Cyan4973]

I think this could work @vtorri.
An important part will be to add a test in AppveyorCI to ensure that the capability works and does not bitrot in the future.

[vtorri]

I'll do a PR this evening. The appveyor part could be added soon. I don't know appveyor, though.

[vtorri]

PR #1914

[Cyan4973]

Adding a make install test to AppveyorCI
to ensure this capability works and will continue to work in the future :
https://github.com/facebook/zstd/pull/1916