[Bug fortran/97084] New: Openmp + Allocatable String Crashes

["wddawson at ucdavis dot edu" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97084

            Bug ID: 97084
           Summary: Openmp + Allocatable String Crashes
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wddawson at ucdavis dot edu
  Target Milestone: ---

Minimal example
```
program test
  implicit none
  integer :: ii
  integer, parameter :: N = 80
  character(len=:), allocatable :: temp_string

  allocate(character(len=N) :: temp_string)

  !$omp parallel default(shared)
  !$omp do
  do ii = 1, N
     temp_string(ii:ii) = "#"
  end do
  !$omp end do
  !$omp end parallel
end program
```

When I compile with `gfortran main.f90 -fopenmp -o test ` I get the following
error:
```
during GIMPLE pass: omplower
main.f90:9:0:

    9 |   !$omp parallel default(shared)
      | 
internal compiler error: in gimplify_expr, at gimplify.c:13885
libbacktrace could not find executable to open
```
It fails with the following compilers:
```
GNU Fortran (Homebrew GCC 10.2.0) 10.2.0
```
```
GNU Fortran (Homebrew GCC 9.3.0) 9.3.0
```
But works with:
```
GNU Fortran (GCC) 4.8.5 20150623 (Red Hat 4.8.5-39)
```

This is possibly related to 89621?