[Bug libstdc++/105915] commit 42eff613 should be backported to gcc-11 for bits/fs_path.h consistency

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105915

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Benda Xu from comment #0)
> With a MWE of
> 
> ```c++
> #include <experimental/filesystem>
> 
> int main(){}
> ```
> would produce
> ```
> /usr/lib/gcc/x86_64-pc-linux-gnu/11.3.1/include/g++-v11/experimental/bits/
> fs_path.h:1209:9: error: 'begin' is missing exception specification
> 'noexcept'
>   path::begin() const
>         ^
> /usr/lib/gcc/x86_64-pc-linux-gnu/11.3.1/include/g++-v11/experimental/bits/
> fs_path.h:428:14: note: previous declaration is here
>     iterator begin() const noexcept;
>              ^
> 
> ```
> on a Gentoo system.

Only when compiling with clang, presumably.