The attached patch adds the error checks similar to the first patch 
previously committed.

I noticed a redundancy in some defines MSGLEN and IOMSG_LEN so I 
consolidated this to one define in io.h. This is just cleanup stuff.

I have added test cases for each of the places where UDTIO is done in 
the library.

Regressions tested on x86_64.

OK for trunk?

Regards,

Jerry

commit 640991bd6b83df4197b2eaec63d1e0e695e48b75
Author: Jerry DeLisle <jvdelisle@gcc.gnu.org>
Date:   Wed Feb 28 20:51:06 2024 -0800

     Fortran: Add user defined error messages for UDTIO.

     The defines IOMSG_LEN and MSGLEN were redundant so these are combined
     into IOMSG_LEN as defined in io.h.

     The remainder of the patch adds checks for when a user defined
     derived type IO procedure sets the IOSTAT or IOMSG variables
     independent of the librrary defined I/O messages.

             PR libfortran/105456

     libgfortran/ChangeLog:

             * io/io.h (IOMSG_LEN): Moved to here.
             * io/list_read.c (MSGLEN): Removed MSGLEN.
             (convert_integer): Changed MSGLEN to IOMSG_LEN.
             (parse_repeat): Likewise.
             (read_logical): Likewise.
             (read_integer): Likewise.
             (read_character): Likewise.
             (parse_real): Likewise.
             (read_complex): Likewise.
             (read_real): Likewise.
             (check_type): Likewise.
             (list_formatted_read_scalar): Adjust to IOMSG_LEN.
             (nml_read_obj): Add user defined error message.
             * io/transfer.c (unformatted_read): Add user defined error
             message.
             (unformatted_write): Add user defined error message.
             (formatted_transfer_scalar_read): Add user defined error 
message.
             (formatted_transfer_scalar_write): Add user defined error 
message.
             * io/write.c (list_formatted_write_scalar): Add user 
defined error message.
             (nml_write_obj): Add user defined error message.

     gcc/testsuite/ChangeLog:

             * gfortran.dg/pr105456-nmlr.f90: New test.
             * gfortran.dg/pr105456-nmlw.f90: New test.
             * gfortran.dg/pr105456-ruf.f90: New test.
             * gfortran.dg/pr105456-wf.f90: New test.
             * gfortran.dg/pr105456-wuf.f90: New test.