Using cpphs 1.18.7, I got the following error with GHC 7.10.1 RC1:

$ cat Main.hs
{-# LANGUAGE CPP #-}

module Main where

main :: IO ()
main = putStrLn "Hello, World!"

$ ghc -pgmP cpphs -optP --cpp Main.hs
...
/usr/local/stow/ghc-7.10.1.RC1/lib/ghc-7.10.0.20141222/include/ghcversion.h:12:30:
    parse error on input ‘\\’

By replacing \\ by \ in ghcversion.h, the issue is fixed.