build: use _LIBCPP_ENABLE_DEBUG_MODE over ENABLE_ASSERTIONS #28479

_LIBCPP_ENABLE_ASSERTIONS is deprecated, and will be removed. See (from libc++ __config in main):

TODO(hardening): remove this in LLVM 19. This is for backward compatibility -- make enabling _LIBCPP_ENABLE_ASSERTIONS (which predates hardening modes) equivalent to setting the safe mode. ifdef _LIBCPP_ENABLE_ASSERTIONS warning "_LIBCPP_ENABLE_ASSERTIONS is deprecated, please use _LIBCPP_ENABLE_SAFE_MODE instead."

From LLVM 17, _LIBCPP_ENABLE_DEBUG_MODE can be used instead, which also performs more checks than safe mode:

Enables the debug mode which contains all the checks from the hardened mode and additionally more expensive checks that may affect the complexity of algorithms. The debug mode is intended to be used for testing, not in production. Mutually exclusive with _LIBCPP_ENABLE_HARDENED_MODE and _LIBCPP_ENABLE_SAFE_MODE.

See https://libcxx.llvm.org/Hardening.html.

Related to #28476.

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Concept ACK. This should fix the warning:

make
Making all in src
make[1]: Entering directory '/bitcoin-core/src'
make[2]: Entering directory '/bitcoin-core/src'
make[3]: Entering directory '/bitcoin-core'
make[3]: Leaving directory '/bitcoin-core'
  CXX      init/bitcoind-bitcoind.o
In file included from init/bitcoind.cpp:5:
In file included from ./common/args.h:8:
In file included from ./common/settings.h:8:
In file included from ./util/fs.h:8:
In file included from ./tinyformat.h:144:
In file included from /usr/lib/llvm-17/bin/../include/c++/v1/algorithm:1739:
In file included from /usr/lib/llvm-17/bin/../include/c++/v1/__assert:13:
/usr/lib/llvm-17/bin/../include/c++/v1/__config:215:6: warning: "_LIBCPP_ENABLE_ASSERTIONS is deprecated, please use _LIBCPP_ENABLE_HARDENED_MODE instead." [-W#warnings]
  215 | #    warning "_LIBCPP_ENABLE_ASSERTIONS is deprecated, please use _LIBCPP_ENABLE_HARDENED_MODE instead."
      |      ^
1 warning generated.

To reproduce on a fresh install of mantic:

export DEBIAN_FRONTEND=noninteractive && apt update && apt install curl wget htop git vim ccache -y && git clone https://github.com/bitcoin/bitcoin.git  --depth=1 ./bitcoin-core && cd bitcoin-core && apt install libc++abi-17-dev libc++-17-dev clang-17 llvm-17 build-essential libtool autotools-dev automake pkg-config bsdmainutils python3-zmq      make automake cmake curl  libtool binutils bsdmainutils pkg-config python3 patch bison        -y  && ( cd depends && make CC=clang-17 CXX="clang++-17 -stdlib=libc++" DEBUG=1 NO_QT=1 NO_WALLET=1 NO_ZMQ=1 NO_UPNP=1 NO_NATPMP=1 -j $(nproc) ) &&  ./autogen.sh && CONFIG_SITE="$PWD/depends/x86_64-pc-linux-gnu/share/config.site" ./configure  && make -j $(nproc)

As a combined follow-up idea, #27495 could be re-opened and re-based?

lgtm ACK 4a825039a509c43ba20b2cd7aab448b3be16bcc3 🙏

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As a combined follow-up idea, #27495 could be re-opened and re-based?

Sure. Reopened and rebased (on master and this and 28476).