Windows linker regression in 1.6

[brson]

As reported here.

I had a problem after upgrading from 1.5 (stable) to 1.6 (stable), so I thought I'd document the fix here. My system is Windows 10, 64-bit; Rust compiler is MSVC ABI; Visual Studio 13 Express for Desktop is installed.

After upgrading, all cargo builds failed with "link.exe could not find ws2_32.lib". The problem was that the LIB path wasn't set. Setting the environment variable LIB to:

"C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\lib\amd64"; "C:\Program Files (x86)\Windows Kits\8.1\Lib\winv6.3\um\x64" fixed the problem. Your paths may vary, of course, and you might have to add other paths if you have other missing libraries.

I'm not sure why this worked with earlier versions of Rust; it seems like it should always have failed.

@retep998 Do you know what we should change to make this work out of the box again?

[retep998]

I have some ideas of what to do that I got after interrogating a different person on IRC about their issues. I will put together a PR that makes that code even more robust.

[alexcrichton]

triage: P-low