[Bug libstdc++/29366] atomics config for sh is weird

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=29366

--- Comment #10 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #9)
> 
> Did this fix things?

No, not entirely.  The whole config/cpu/sh/atomicity.h header should not be
required, but because of PR 53579, it is.

Please do not close any SH related PR's just for the sake of reducing the
number of PR's.  I keep them open because they are actual issues.