[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 #8 from Janne Blomqvist <jb at gcc dot gnu.org> ---
Actually, wasn't this simple as the above patch broke the synchronous version.
Need to think more what to do.