I just tried this and compiled ok.
#pragma list off
#pragma  intrinsic hpsortinit

int main ( int argc, char* argv [], char* e[], int parm, char* info ){
   long  stat;
   char  buf [1000];
   int   keys [] = { 1, 10, 0, 0 };

   hpsortinit ( &stat,,,, sizeof ( buf ),, 1, keys );
}
/*----------------------------------------------------------------*/

So I checked my CCOPTS var
SHOWVAR CCOPTS
CCOPTS = -Aa -C +e -D_SOCKET_SOURCE

The -Aa option says compile with ANSI standards.
The -C options says to leave comments in the code listing (I think)
The +e option says allow extensions **** This is what I think you need
to allow missing parameters.
The -D  defines a name

This is in the HP/C Programmers Manual:
HP C Extensions to ANSI C (+e)

There are a number of HP C extensions enabled by the +e option in ANSI
mode:

   *   Long pointers.
   *   Dollar sign character $ in an identifier.
   *   Compiler supplied defaults for missing arguments to intrinsic
       calls (For example FOPEN("filename",fopt,,rsize), where ,,
       indicates that the missing aopt parameter is automatically
       supplied with default values.)
   *   Sized enumerated types:  char enum, short enum, int enum, and
long
       enum.
   *   Long long integer type.  Note, the long long data type is only
       available in HP C Series 700/800.

These are the only HP C extensions that require using the +e option.

When coding for portability, you should compile your programs without
the
+e command line option, and rewrite code that causes the compiler to
generate messages related to HP C extensions.

*********************
* Keven Miller   KC7LYD
* [log in to unmask]   (Salt Lake City, Utah, USA)
* ICQ 5721825
*********************