pkg/56240: octave 6.2.0 fails to build on NetBSD-current

[prlw1%cam.ac.uk@localhost]

>Number:         56240
>Category:       pkg
>Synopsis:       octave 6.2.0 fails to build on NetBSD-current
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 07 09:00:01 +0000 2021
>Originator:     Patrick Welche
>Release:        pkgsrc of 3 June 2021  (no octave change 7 June)
>Organization:
>Environment:
NetBSD-9.99.83/amd64
>Description:
octave 6.2.0 build fails with

  CXX      libinterp/corefcn/libcorefcn_la-getrusage.lo
libinterp/corefcn/file-io.cc: In function 'octave::stream do_stream_open(const string&, const string&, const string&, std::string, int&)':
libinterp/corefcn/file-io.cc:409:37: error: invalid conversion from 'void*' to 'iconv_t' {aka '__tag_iconv_t*'} [-fpermissive]
  409 |         octave_iconv_close_wrapper (codec);
      |                                     ^~~~~
      |                                     |
      |                                     void*
In file included from libinterp/corefcn/file-io.cc:56:
./liboctave/wrappers/iconv-wrappers.h:39:37: note:   initializing argument 1 of 'int octave_iconv_close_wrapper(iconv_t)'
   39 | octave_iconv_close_wrapper (iconv_t cd);
      |                             ~~~~~~~~^~
  CXX      libinterp/corefcn/libcorefcn_la-givens.lo
  CXX      libinterp/corefcn/libcorefcn_la-gl-render.lo
  CXX      libinterp/corefcn/libcorefcn_la-gl2ps-print.lo
gmake[2]: *** [Makefile:18865: libinterp/corefcn/libcorefcn_la-file-io.lo] Error 1
gmake[2]: *** Waiting for unfinished jobs....
gmake[2]: Leaving directory '/tmp/pkgsrc/math/octave/work.x86_64/octave-6.2.0'
gmake[1]: *** [Makefile:27517: all-recursive] Error 1
gmake[1]: Leaving directory '/tmp/pkgsrc/math/octave/work.x86_64/octave-6.2.0'
gmake: *** [Makefile:11142: all] Error 2
*** Error code 2

>How-To-Repeat:
cd /usr/pkgsrc/math/octave
make
>Fix: