Investigate std.net.curl access violation on Windows with and older dmd/phobos

[mihails-strasuns]

Split from #48

For some reason when using older (e.g. 2.089) dmd, providing both 32-bit and 64-bit libcurl.dll via PATH result in an Access Violation. Root cause is not clear - I was not able to reproduce the problem on my local Windows machine with the same dmd archive.

Further investigation requires rebuilding Phobos with debug symbols for CI and currently is a low priority.