Found the following significant warnings:
  ../src/s2/util/coding/coder.h:161:52: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = char*; T2 = char*]’ is deprecated [-Wdeprecated-declarations]
  ../src/s2/util/coding/coder.h:493:65: warning: ‘using absl::debian10::is_trivially_copy_constructible = struct std::is_trivially_copy_constructible<Decoder>’ is deprecated [-Wdeprecated-declarations]
  ../src/s2/util/coding/coder.h:495:62: warning: ‘using absl::debian10::is_trivially_copy_assignable = struct std::is_trivially_copy_assignable<Decoder>’ is deprecated [-Wdeprecated-declarations]
  ../src/s2/util/coding/coder.h:497:59: warning: ‘using absl::debian10::is_trivially_destructible = struct std::is_trivially_destructible<Decoder>’ is deprecated [-Wdeprecated-declarations]
  ../src/s2/util/math/vector.h:62:34: warning: ‘using absl::debian10::make_index_sequence = std::make_index_sequence<N>’ is deprecated: Use std::make_index_sequence instead. [-Wdeprecated-declarations]
  ../src/s2/util/math/vector.h:62:56: warning: ‘using absl::debian10::make_index_sequence = std::make_index_sequence<N>’ is deprecated: Use std::make_index_sequence instead. [-Wdeprecated-declarations]
  s2/mutable_s2shape_index.cc:470:46: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/mutable_s2shape_index.cc:483:44: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2lax_loop_shape.cc:38:35: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2lax_loop_shape.cc:43:33: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2lax_loop_shape.cc:95:35: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2lax_loop_shape.cc:102:33: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2loop.cc:113:28: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2loop.cc:114:35: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2loop.cc:132:26: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/s2loop.cc:133:33: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = int; T2 = int]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:35:26: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:36:28: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:37:40: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:38:27: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:43:24: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:44:26: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:45:38: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
  s2/util/coding/coder.cc:46:25: warning: ‘constexpr T1 absl::debian10::exchange(T1&, T2&&) [with T1 = unsigned char*; T2 = std::nullptr_t]’ is deprecated [-Wdeprecated-declarations]
See ‘/home/hornik/tmp/R.check/r-devel-gcc/Work/PKGS/s2.Rcheck/00install.out’ for details.
* used C compiler: ‘gcc-16 (Debian 16.1.0-2) 16.1.0’
* used C++ compiler: ‘g++-16 (Debian 16.1.0-2) 16.1.0’