Change C-style comments to Haskell-style.

Change C-style comments to Haskell-style.
These two headers are only ever used for pre-processing Haskell code,
and are never seen by any C tools except cpp.  Using the Haskell comment
convention means that cpphs no longer needs to be given the --strip
option to remove C comments from open code.  This is a Good Thing,
because all of /* */ and // are valid Haskell operator names, and there
is no compelling reason to forbid using them in files which also happen
to have C-preprocessor directives.