VMS Help CC, /ASSUME  *Conan The Librarian (sorry for the slow response - running on an old VAX)

     /ASSUME=(option[,...])

  Controls compiler assumptions.  You may select the following
  options:

     [NO]EXACT_CDD_OFFSETS

        Controls the alignment of Control Data Dictionary records.

        If /ASSUME=EXACT_CDD_OFFSETS is specified, the records input
        from the CDD are given the exact alignment (relative to the
        start of the record) specified by the CDD definition.  This
        alignment is independent of the current compiler
        member-alignment setting.

        If /ASSUME=NOEXACT_CDD_OFFSETS is specified, the compiler may
        modify the offsets specified in a CDD record according to the
        current member-alignment setting.

        The default is /ASSUME=NOEXACT_CDD_OFFSETS.

     [NO]HEADER_TYPE_DEFAULT

        Specifies whether the default file-type mechanism (.h) for
        header files is enabled (HEADER_TYPE_DEFAULT) or disabled
        (NOHEADER_TYPE_DEFAULT).

        The default is /ASSUME=HEADER_TYPE_DEFAULT.

     [NO]WRITABLE_STRING_LITERALS

        Stores string constants in a writable psect.  Otherwise, such
        constants will be placed in non-writable psect.

        For /STANDARD=VAXC or /STANDARD=COMMON, the default is
        /ASSUME=WRITABLE_STRING_LITERALS.  For all other compiler
        modes, the default is /ASSUME=NOWRITABLE_STRING_LITERALS.