/EXTERN_MODEL=option
     /EXTERN_MODEL=RELAXED_REFDEF (D)

  In conjunction with the /SHARE_GLOBALS qualifier, controls the
  initial extern model of the compiler.  Conceptually, the compiler
  behaves as if the first line of the program being compiled was a
  #pragma extern_model directive with the model and psect name, if
  any, specified by the /EXTERN_MODEL qualifier and with the shr or
  noshr keyword specified by the /SHARE_GLOBALS qualifier.

  For example, assume the command line contains the following
  qualifier:

       /EXTERN_MODEL=STRICT_REFDEF="MYDATA"/NOSHARE

  The compiler will act as if the program began with the following
  line:

       #pragma extern_model strict_refdef "MYDATA" noshr

  See also #pragma extern_model.

  The /EXTERN_MODEL qualifier takes the following options, which have
  the same meaning as for the #pragma extern_model directive:

  COMMON_BLOCK

  RELAXED_REFDEF

  STRICT_REFDEF

  STRICT_REFDEF="NAME"

  GLOBALVALUE

  The default model on VSI C is relaxed/refdef with the noshare
  attribute.  This is different from the model used by VAX C, which
  is common block, share.