/sys$common/syshlp/helplib.hlb CC, /PREPROCESS_ONLY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

     /PREPROCESS_ONLY[=filename]
     /NOPREPROCESS_ONLY (D)

  Causes the compiler to perform only the actions of the preprocessor
  phase and write the resulting processed text out to a file.