Merge bitcoin#30821: build: work around issue with Boost <= 1.80 and Clang >= 18

cd062d6 build: work around issue with Boost <= 1.80 and Clang >= 18 (fanquake)

Pull request description:

  Our current minimum supported Boost is `1.73.0`. However, when compiling with Boost `1.74.0` (Debian Stable), using Clang `18`, compilation fails with:
  ```bash
  In file included from /usr/include/boost/mpl/integral_c.hpp:32:
  /usr/include/boost/mpl/aux_/integral_wrapper.hpp:73:31: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'udt_builtin_mixture_enum' [-Wenum-constexpr-conversion]
     73 |     typedef AUX_WRAPPER_INST( BOOST_MPL_AUX_STATIC_CAST(AUX_WRAPPER_VALUE_TYPE, (value - 1)) ) prior;
        |                               ^
  /usr/include/boost/mpl/aux_/static_cast.hpp:24:47: note: expanded from macro 'BOOST_MPL_AUX_STATIC_CAST'
     24 | #   define BOOST_MPL_AUX_STATIC_CAST(T, expr) static_cast<T>(expr)
        |                                               ^
  In file included from ../../../src/test/validation_chainstatemanager_tests.cpp:8:
  In file included from ../../../src/node/chainstatemanager_args.h:9:
  In file included from ../../../src/validation.h:28:
  In file included from ../../../src/txmempool.h:26:
  In file included from /usr/include/boost/multi_index/hashed_index.hpp:38:
  In file included from /usr/include/boost/multi_index/detail/node_handle.hpp:22:
  In file included from /usr/include/boost/multi_index_container_fwd.hpp:18:
  In file included from /usr/include/boost/multi_index/indexed_by.hpp:17:
  In file included from /usr/include/boost/mpl/vector.hpp:36:
  In file included from /usr/include/boost/mpl/vector/vector20.hpp:18:
  In file included from /usr/include/boost/mpl/vector/vector10.hpp:18:
  In file included from /usr/include/boost/mpl/vector/vector0.hpp:24:
  In file included from /usr/include/boost/mpl/vector/aux_/clear.hpp:18:
  In file included from /usr/include/boost/mpl/vector/aux_/vector0.hpp:22:
  In file included from /usr/include/boost/mpl/vector/aux_/iterator.hpp:19:
  In file included from /usr/include/boost/mpl/plus.hpp:19:
  In file included from /usr/include/boost/mpl/aux_/arithmetic_op.hpp:17:
  In file included from /usr/include/boost/mpl/integral_c.hpp:32:
  /usr/include/boost/mpl/aux_/integral_wrapper.hpp:73:31: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'int_float_mixture_enum' [-Wenum-constexpr-conversion]
  /usr/include/boost/mpl/aux_/static_cast.hpp:24:47: note: expanded from macro 'BOOST_MPL_AUX_STATIC_CAST'
     24 | #   define BOOST_MPL_AUX_STATIC_CAST(T, expr) static_cast<T>(expr)
        |                                               ^
  2 errors generated.
  ```

  Work around this issue by ignoring this diagnostic for this include. I did attempt to just downgrade the error into a warning, but that did not seem to work. Not a huge fan of inline warning/issue suppression, but this seems like the cleanest thing to do here (and easy to backport to `28.x`).

  Can be tested with something like:
  ```bash
  docker pull debian:bookworm
  docker run -it debian:bookworm /bin/bash

  apt update &&  apt install ccache cmake git pkg-config libboost-dev libevent-dev python3 libsqlite3-dev lsb-release wget software-properties-common gnupg
  git clone https://github.com/bitcoin/bitcoin

  wget https://apt.llvm.org/llvm.sh
  chmod +x llvm.sh
  ./llvm.sh 18

  cd bitcoin
  cmake -B build -DCMAKE_C_COMPILER=clang-18 -DCMAKE_CXX_COMPILER=clang++-18
  cmake --build build -j17
  <snip>
  In file included from /usr/include/boost/mpl/integral_c.hpp:32:
  /usr/include/boost/mpl/aux_/integral_wrapper.hpp:73:31: error: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'int_float_mixture_enum' [-Wenum-constexpr-conversion]
  /usr/include/boost/mpl/aux_/static_cast.hpp:24:47: note: expanded from macro 'BOOST_MPL_AUX_STATIC_CAST'
     24 | #   define BOOST_MPL_AUX_STATIC_CAST(T, expr) static_cast<T>(expr)
        |                                               ^
  2 errors generated.

  Apply the patch

  cmake --build build -j17
  ctest --test-dir build -j17
  ```

  Fixes bitcoin#30751.

ACKs for top commit:
  achow101:
    ACK cd062d6
  hebasto:
    ACK cd062d6, tested on Fedora 40 using the downloaded [Boost 1.74](https://archives.boost.io/release/1.74.0/source/) and commands as follows:

Tree-SHA512: 13e5b3a544496ed2a6529ad45d03a2d872ebf41caaa06d0eec23a639d678ae1c55d73f2d4b164a4cc9e2c163264e736cd85eae90fde8089ca999cd810b16ecb5

Author: achow101

src/txmempool.h

@@ -23,7 +23,17 @@
 #include <util/result.h>
 #include <util/feefrac.h>
 
+// This works around a bug in Boost <= 1.80.0 when using Clang >=18.
+// See https://github.com/bitcoin/bitcoin/issues/30751.
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wenum-constexpr-conversion"
+#endif
 #include <boost/multi_index/hashed_index.hpp>
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+
 #include <boost/multi_index/identity.hpp>
 #include <boost/multi_index/indexed_by.hpp>
 #include <boost/multi_index/ordered_index.hpp>