+dnl Check for Happy and version. If we're building GHC, then we need
+dnl at least Happy version 1.6. If there's no installed Happy, we look
+dnl for a happy source tree and point the build system at that instead.
+dnl
+dnl ToDo: when we reset HappyCmd to the source tree, autoconf doesn't
+dnl seems to insert it in the cache file. sigh.