Windows support through vcpkg

[ethanhs]

I can set up CI for this a bit later, but I wanted to hear your thoughts on this as a solution to Windows support.

[termoshtt]

Good suggestion 👍

vcpkg looks to be better choice than the ways in the wiki page of OpenBLAS. This is a good start point to support Windows, though we have still a problem, to manage CBLAS and LAPACKE flags, and architecture problem discussed in OpenMathLib/OpenBLAS#2256. These problems should be other issues, and I think it is better to merge this PR as it is with some minor fix and CI setup.

[ethanhs]

Okay I believe I have resolved all of the things @termoshtt requested. I still need to make CI work. Is MSYS a supported platform? I'm not sure how to detect this. Perhaps target_os = windows but target_family=unix? I'll have to look into it. Perhaps do detection based on the compiler triple if I can do that?

[termoshtt]

I'm not sure how to detect this. Perhaps target_os = windows but target_family=unix?

Good catch 💯
There are two types of windows ABI: *-windows-msvc and *-windows-gnu. https://forge.rust-lang.org/release/platform-support.html MSYS2 (mingw-w64) is referred as x86_64-pc-windows-gnu in Rust , and thus you can detect them by target_env.

Is MSYS a supported platform?

Although the CI of master currently fails (#38), it should be supported. So the build way matrix is here:

SYSTEM flag	windows-msvc	windows-gnu, UNIX systems
TRUE	vcpkg	Seek system shared libs and link it
FALSE	not supported yet	Build OpenBLAS by gcc-toolchain and link it

This table suggests us that we should switch by msvc and others. Could you fix them?

If you are not familiar with AppVeyor, feel free to let me know. I will fix them with #38

[ethanhs]

@termoshtt feel free to fix CI, I'm not familiar enough with Appveyor CI to set up vcpkg and it seems the msys builds are broken too.

[IvanUkhov]

Appveyor is a project in itself. I don’t think it ever worked for this repository. There is also an issue for this; see #38.

[termoshtt]

Thanks a lot!

[ethanhs]

Absolutely, I'll rebase #37 on this and add the feature next :)