Remove double quotes around searchPath elements on Windows

The GHC source code contains 2 custom ([buggy](https://ghc.haskell.org/trac/ghc/ticket/9698)) implementations of splitSearchPath. I would like to replace them by filepath's version. This patch is needed to make filepath's version feature complete with the GHC versions.

What do you think? I'm not sure why the GHC version actually has this feature, but someone's code might break if I remove it.

Side note: it feels kind of dirty having to commit a 340 line patch, with 99% trivial test linenumber changes.