[flang][runtime] PAUSE statement does not actually pause program

[foxtran]

Execution of the following program is not suspending, when PAUSE statement is executed:

program pause_test
   do i = 1, 5
     print *, i
     PAUSE 12
   end do
end program pause_test

Meantime, libgfortran requests to type go to continue execution.

See an example here:
https://godbolt.org/z/nenPKKx9h

[eugeneepshteyn]

flang FRTL checks that it's running in a terminal to do PAUSE action. When running in a terminal:

$ flang pause.f90 && ./a.out
 1
Fortran PAUSE: hit RETURN to continue:
 2
Fortran PAUSE: hit RETURN to continue:
 3
Fortran PAUSE: hit RETURN to continue:
 4
Fortran PAUSE: hit RETURN to continue:
 5
Fortran PAUSE: hit RETURN to continue:

I suspect that Compiler Explorer environment fails isatty(0) check.

[llvmbot]

@llvm/issue-subscribers-flang-runtime

Author: foxtran (foxtran)

Execution of the following program is not suspending, when PAUSE statement is executed: ``` program pause_test do i = 1, 5 print *, i PAUSE 12 end do end program pause_test ```

Meantime, libgfortran requests to type go to continue execution.

See an example here:
https://godbolt.org/z/nenPKKx9h