[Bug libfortran/90038] execute_command_line should not use fork()

[jb at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90038

--- Comment #3 from Janne Blomqvist <jb at gcc dot gnu.org> ---
Further testing revealed that it leaves zombie processes around as the child is
never wait()'ed for. E.g.

program cmd
  implicit none
  call execute_command_line("echo hi", wait=.FALSE.)
  call sleep(30)
end program cmd