[BUG] FTB with Debian Bullseye g++ 10.2.1-6

[mralusw]

Version of Kakoune

master (9acd4e62)

Reproducer

On MX Linux (really Debian GNU/Linux 11 (bullseye)), with g++ --version = g++ (Debian 10.2.1-6) 10.2.1 20210110

git clean -fdx
make

Outcome

...
g++  -O3 -pedantic -std=c++2a -g -Wall -Wextra -Wno-unused-parameter -Wno-sign-compare -Wno-address -Wno-init-list-lifetime -MD -MP -MF .client.opt.d -c -o .client.opt.o client.cc
In file included from face_registry.hh:5,
                 from scope.hh:5,
                 from buffer.hh:12,
                 from selection.hh:4,
                 from context.hh:4,
                 from input_handler.hh:6,
                 from client.hh:7,
                 from client.cc:1:
utils.hh: In instantiation of ‘Kakoune::FunctionRef<Res(Args ...)>::FunctionRef(Target&&) [with Target = Kakoune::Client::generate_mode_line() const::<lambda(Kakoune::String)>; Res = Kakoune::String; Args = {Kakoune::String}]’:
client.cc:161:77:   required from here
utils.hh:181:31: internal compiler error: in tsubst_pack_expansion, at cp/pt.c:12930
  181 |             requires not std::is_same_v<FunctionRef, std::remove_cvref_t<Target>>;
      |                          ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0x7f4abada7d09 __libc_start_main
        ../csu/libc-start.c:308
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-10/README.Bugs> for instructions.
make[1]: *** [Makefile:104: .client.opt.o] Error 1
make[1]: Leaving directory '/tmp/kak-build/src'
make: *** [Makefile:2: all] Error 2

Expectations

should build, or requirement should be documented

Additional information

Build works with g++-10 from Ubuntu Focal (g++-10 (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0)

Also, no problems with clang++-12, clang++-13

[vbauerster]

There is same build error on arch linux (g++ (GCC) 10.2.0).