MSVC flexlink appears to attempt cygpath #139
Description
From a report on a private channel, flexlink appears to fallback to calling cygpath if it fails to find .lib files (e.g. ws2_32.lib).
Possibly repro case is to configure OCaml as normal, then unset LIB and attempt to build.
Not clear if this is a regression, possibly from #118, or if it's just always been wrong.