For the exit processing only members of _GLOBAL_REENT were used by default. If
the _REENT_GLOBAL_ATEXIT option was enabled, then the data structures were
provided through dedicated global objects. Make this option the default.
Remove the option. Rename struct _reent members _atexit and _atexit0 to
_reserved_6 and _reserved_7, respectively. Provide them only if
_REENT_BACKWARD_BINARY_COMPAT is defined.
2faeaf50fd