[flang] Missing diagnostic on DECIMAL= appear with FORM='UNFORMATTED'

[DanielCChen]

Consider the following code:

      integer :: ios

      open(1, form='unformatted', decimal='comma', iostat=ios)

      ! test 9: decimal= specifier is not allowed in unformatted i/o
      if( ios == 0 ) then
         ERROR STOP 1
      endif

      end

The decimal= specifier can only appear on formatted I/O.

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Daniel Chen (DanielCChen)

Consider the following code: ``` integer :: ios

  open(1, form='unformatted', decimal='comma', iostat=ios)

  ! test 9: decimal= specifier is not allowed in unformatted i/o
  if( ios == 0 ) then
     ERROR STOP 1
  endif

  end

The `decimal=` specifier can only appear on formatted I/O. 
</details>

[eugeneepshteyn]

Agreed, F23, 12.5.6.7, states "The DECIMAL= specifier is permitted only a connection for formatted input/output."