Bug#1050684: /usr/lib/llvm-14/bin/clang: Default clang++ -std=c++20 does not work with default libstdc++ on trixie

[debian.doorbell912 at slmail.me]

Package: clang-14
Version: 1:14.0.6-13
Severity: important
File: /usr/lib/llvm-14/bin/clang

Dear Maintainer,

The default clang++ version on trixie and sid is 14. However, this
version of clang++ does not go well with C++20 and the default
libstdc++ (version 13).

It would be good to bump the default clang version to 15, or 16 (both
of which are already available in trixie), or even clang-17, once and
if it is released.

Steps to reproduce bug on a fresh install of Debian Trixie:

cat t.cpp && clang++ --version && clang++ -std=c++20 -o t -Weverything t.cpp

#include <chrono>
int main() { return 0; }

Debian clang version 14.0.6
Target: aarch64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

In file included from t.cpp:1:
/usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48:
error: call to consteval function
'std::chrono::hh_mm_ss::_S_fractional_width' is not a constant
expression
        static constexpr unsigned fractional_width = {_S_fractional_width()};
                                                      ^
/usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/chrono:2320:48:
note: undefined function '_S_fractional_width' cannot be used in a
constant expression
/usr/bin/../lib/gcc/aarch64-linux-gnu/13/../../../../include/c++/13/chrono:2275:2:
note: declared here
        _S_fractional_width()
        ^
1 error generated.



-- System Information:
Debian Release: trixie/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: arm64 (aarch64)

Versions of packages clang-14 depends on:
ii  binutils                2.41-4
ii  libc6                   2.37-7
ii  libc6-dev               2.37-7
ii  libclang-common-14-dev  1:14.0.6-13
ii  libclang-cpp14          1:14.0.6-13
ii  libclang1-14            1:14.0.6-13
ii  libgcc-13-dev           13.2.0-2
ii  libgcc-s1               13.2.0-2
ii  libllvm14               1:14.0.6-13
ii  libobjc-13-dev          13.2.0-2
ii  libstdc++-13-dev        13.2.0-2
ii  libstdc++6              13.2.0-2
ii  llvm-14-linker-tools    1:14.0.6-13