#36042 build: Bump g++ minimum supported version to 13

• Bump minimum supported compiler to GCC 13.1, dropping unsupported GCC 12
• Enables modern C++ features across the codebase such as std::format and eventual C++23 adoption

Bumps the minimum required GCC version to 13.1 in doc/dependencies.md and CMake. Adds a CMake check for C++20 std::format, updates CI images and configuration scripts to GCC 13+ (including NetBSD cross-compilation setup), and converts an example benchmark to std::format.

Problem: Bitcoin Core cannot currently use C++20 std::format or advance to C++23 because supported compiler toolchains still include GCC 12 (which is now EOL upstream and lacks std::format).

P3 · unblocks #36033

• P3 because it unblocks C++20 std::format and future C++23 adoption across the codebase
• Targeted for v33.x making the toolchain bump deferrable

Raises minimum toolchain requirements to GCC 13.1, dropping unsupported GCC 12 and unblocking C++20 std::format and C++23 PRs (#36033). However, the author explicitly noted this is targeted for v33.x next year, making the work reasonably deferrable.

Membership: Directly changes compiler version requirements in CMake, doc/dependencies.md, and CI build scripts.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 2

• Review #36052 first
• Needs rebase due to merge conflicts with master

The PR has merge conflicts with master (mergeable_state is dirty) and has the Needs rebase label.

Author status: active, last force-pushed on 2026-08-24

Resolved concerns:

• NetBSD cross-compilation CI compatibility resolved by downloading NetBSD gcc14 packages for libstdc++-14 headers and runtime.

• Concept approval and verified native GCC package behavior on NetBSD (hebasto)
• No objections raised during discussion on compiler support (fanquake, maflcko)

Strong support: Concept ACK and NetBSD native verification from hebasto without objection.

hebasto verified native GCC 15 package behavior on NetBSD 11.0 and provided a Concept ACK; no objections have been raised.

• hebasto tested native NetBSD GCC package compilation and posted 'Concept ACK.' on 2026-08-24.
• fanquake and maflcko discussed compiler support on NetBSD without disagreement on the goal.

Review verdicts (DrahtBot): 0

• Concept ACK: hebasto

Depends on: #36052

Enables:

• #36033

Based on (shares commits with): #36052

235 lines under test/bench/ci.

• ci/test/00_setup_env_native_previous_releases.sh +11/-12
• cmake/module/CheckCXXFeatures.cmake +18/-0
• ci/test/00_setup_env_netbsd_cross.sh +11/-5
• ci/test/00_setup_env_native_asan.sh +7/-7
• ci/test/00_setup_env_native_fuzz_with_msan.sh +6/-7
• ci/test/00_setup_env_native_msan.sh +6/-7
• ci/test/01_base_install.sh +12/-0
• ci/test/00_setup_env_arm.sh +5/-5
• ci/test/00_setup_env_native_valgrind.sh +4/-5
• ci/test/00_setup_env_native_fuzz.sh +4/-4
• ci/test/00_setup_env_native_tidy.sh +4/-4
• ci/test/00_setup_env_riscv_bare_cross.sh +4/-3
• ci/test/00_setup_env_freebsd_cross.sh +3/-3
• ci/test/00_setup_env_i686_no_ipc.sh +3/-3
• ci/test/00_setup_env_mac_cross.sh +3/-3
• ci/test/00_setup_env_mac_cross_intel.sh +3/-3
• ci/test/00_setup_env_mac_native.sh +3/-3
• ci/test/00_setup_env_mac_native_fuzz.sh +5/-1
• ci/test/00_setup_env_native_alpine_musl.sh +3/-3
• ci/test/00_setup_env_native_chimera_lto.sh +3/-3
• ci/test/00_setup_env_native_fuzz_with_valgrind.sh +3/-3
• ci/test/00_setup_env_native_iwyu.sh +3/-3
• ci/test/00_setup_env_native_nowallet.sh +3/-3
• ci/test/00_setup_env_native_tsan.sh +3/-3
• ci/test/00_setup_env_openbsd_cross.sh +3/-3
• ci/test/00_setup_env_s390x.sh +3/-3
• ci/test/00_setup_env_win64.sh +3/-3
• ci/test/00_setup_env_win64_msvcrt.sh +3/-3
• src/bench/wallet_migration.cpp +3/-3
• doc/release-notes-36042.md +4/-0
• doc/dependencies.md +1/-1
• doc/build-windows.md +0/-1

PR 36042 raises the minimum supported GCC compiler version from 12.1 to 13.1 in CMake and updates CI test images and configurations accordingly. This change enables the project to use C++20 std::format and lays groundwork for requiring C++23 in a future release cycle (targeted for v33.x in 2027). hebasto verified NetBSD compatibility and gave a Concept ACK. The PR currently has merge conflicts and is awaiting a rebase.