/PLUS_LIST_OPTIMIZE
     /NOPLUS_LIST_OPTIMIZE (D)

  Provides improved optimization and code generation across file
  boundaries that would not be available if the files were compiled
  seperately.

  When you specify /PLUS_LIST_OPTIMIZE on the command line in
  conjunction with a series of file specifications separated by plus
  signs, the compiler does not concatenate each of the specified
  source files together.  Instead, each file is treated separately
  for purposes of parsing, except that the compiler will issue
  diagnostics about conflicting external declarations and function
  definitions that occur in different files.  For purposes of code
  generation, the compiler treats the files as one application.

  The default is /NOPLUS_LIST_OPTIMIZE.