The <ranges> header was added to the freestanding headers in
r16-3575-g1a41e52d7ecb58 but bits/binders.h that it depends on was not
moved, making <ranges> unusable with --disable-libstdcxx-hosted.
libstdc++-v3/ChangeLog:
PR libstdc++/125112
* include/Makefile.am: Move bits/binders.h from bits_headers to
bits_freestanding.
* include/Makefile.in: