Boost compilation fails with Clang 18.1 in ossfuzz

[r0qs]

After updating the Boost download URL in #15691 we encountered the root cause of this issue again: #15338

I investigate it further and in summary, compiling Boost version 1.74 fails when using the current default Clang version (18.1.8) in the ossfuzz base image:

96.21 In file included from /usr/src/boost_1_74_0/boost/math/special_functions/bessel.hpp:24:
96.21 In file included from /usr/src/boost_1_74_0/boost/math/special_functions/detail/bessel_ik.hpp:13:
96.21 /usr/src/boost_1_74_0/boost/math/special_functions/round.hpp:118:12: warning: implicit conversion from 'type' (aka 'long long') to 'double' changes value from 9223372036854775807 to 9223372036854775808 [-Wimplicit-const-int-float-conversion]
96.21   118 |    if((r > (std::numeric_limits<boost::long_long_type>::max)()) || (r < (std::numeric_limits<boost::long_long_type>::min)()))
96.21       |          ~ ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
96.21 libs/math/build/../src/tr1/c_policy.hpp:129:1: note: in instantiation of function template specialization 'boost::math::llround<double, boost::math::policies::policy<domain_error<errno_on_error>, pole_error<errno_on_error>, overflow_error<errno_on_error>, evaluation_error<errno_on_error>, rounding_error<errno_on_error>, default_policy, default_policy, default_policy, default_policy, default_policy, default_policy>>' requested here
96.21   129 | BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS(c_policy)
96.21       | ^
96.21 /usr/src/boost_1_74_0/boost/math/special_functions/math_fwd.hpp:1151:4: note: expanded from macro 'BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS'
96.21  1151 |    BOOST_MATH_DETAIL_LL_FUNC(Policy)\
96.21       |    ^
96.21 /usr/src/boost_1_74_0/boost/math/special_functions/math_fwd.hpp:1133:89: note: expanded from macro 'BOOST_MATH_DETAIL_LL_FUNC'
96.21  1133 |    inline boost::long_long_type llround(const T& v){ using boost::math::llround; return llround(v, Policy()); }\
96.21       |                                                                                         ^
96.21 libs/math/build/../src/tr1/llround.cpp:18:23: note: in instantiation of function template specialization 'c_policies::llround<double>' requested here
96.21    18 |    return c_policies::llround BOOST_PREVENT_MACRO_SUBSTITUTION(x);
96.21       |                       ^
96.21 1 warning generated.
96.21 clang-linux.compile.c++.with-pch bin.v2/libs/math/build/clang-linux-18.1.8/release/link-static/threading-multi/visibility-hidden/lround.o
96.21 In file included from libs/math/build/../src/tr1/lround.cpp:1:
96.21 In file included from /usr/src/boost_1_74_0/libs/math/build/../src/tr1/pch.hpp:9:

This issue seems to have started when ossfuzz updated their LLVM version to 18 (google/oss-fuzz#11714) as observed by @nikola-matic in #15338.
When upgrading Boost to version 1.83, CMake fails to locate the libc++ headers:

69.20 In file included from /usr/local/bin/../include/c++/v1/__assertion_handler:13:
69.20 /usr/local/bin/../include/c++/v1/__config:13:10: fatal error: '__config_site' file not found
69.20    13 | #include <__config_site>
69.20       |          ^~~~~~~~~~~~~~~
69.20 1 error generated.
69.51
69.51     "clang++"   -fvisibility-inlines-hidden -m64 -pthread -O3 -Wall -fvisibility=hidden -Wno-inline --target=x86_64-pc-linux -stdlib=libc++ -pthread -DBOOST_ALL_NO_LIB=1 -DBOOST_ATOMIC_SOURCE -DBOOST_ATOMIC_STATIC_LINK=1 -DNDEBUG   -I"." -I"libs/atomic/src"  -c -o "bin.v2/libs/atomic/build/clang-linux-18/release/link-static/threading-multi/visibility-hidden/lock_pool.o" "libs/atomic/src/lock_pool.cpp"

This can be resolved by installing libc++ development files and correcting its paths, e.g.:

    CXXFLAGS="-stdlib=libc++ -pthread -I/usr/include/c++/v1" LDFLAGS="-stdlib=libc++ -lc++abi" ./bootstrap.sh --with-toolset=clang --prefix=/usr; \
    ./b2 toolset=clang cxxflags="-stdlib=libc++ -pthread -I/usr/include/c++/v1" linkflags="-stdlib=libc++ -pthread -lc++abi" headers; \
    ./b2 toolset=clang cxxflags="-stdlib=libc++ -pthread -I/usr/include/c++/v1" linkflags="-stdlib=libc++ -pthread -lc++abi" \

However, Boost will fail again because of incompatibility with the C++ standard library:

9.12 In file included from ./boost/predef/detail/_exception.h:12:
69.12 In file included from /usr/include/c++/v1/exception:82:
69.12 In file included from /usr/include/c++/v1/__exception/exception_ptr.h:16:
69.12 In file included from /usr/include/c++/v1/__memory/construct_at.h:23:
69.12 /usr/include/c++/v1/new:216:86: error: reference to unresolved using declaration
69.12   216 | _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_OVERRIDABLE_FUNC_VIS void* operator new[](std::size_t __sz) _THROW_BAD_ALLOC;
69.12       |                                                                                      ^
69.12 /usr/include/c++/v1/cstdlib:103:1: note: using declaration annotated with 'using_if_exists' here
69.12   103 | using ::size_t _LIBCPP_USING_IF_EXISTS;
69.12       | ^
69.12 In file included from libs/chrono/src/process_cpu_clocks.cpp:17:
69.12 In file included from ./boost/chrono/detail/inlined/process_cpu_clocks.hpp:15:
69.12 In file included from ./boost/chrono/config.hpp:17:
69.12 In file included from ./boost/predef.h:16:
69.12 In file included from ./boost/predef/library.h:14:
69.12 In file included from ./boost/predef/library/std.h:12:
69.12 In file included from ./boost/predef/library/std/_prefix.h:21:
69.12 In file included from ./boost/predef/detail/_exception.h:12:

By the way, why do we actually use libc++ and not the standard libstdc++? The base image is a Ubuntu 20.04 machine anyway. And, it can successfully compile Boost 1.83 using libstdc++ and Clang-18. For example, the diff below fix the issue without downgrading clang. But maybe libc++ is a requirement of ossfuzz?

diff --git a/scripts/docker/buildpack-deps/Dockerfile.ubuntu.clang.ossfuzz b/scripts/docker/buildpack-deps/Dockerfile.ubuntu.clang.ossfuzz
index 743d924d7..170c2ebcd 100644
--- a/scripts/docker/buildpack-deps/Dockerfile.ubuntu.clang.ossfuzz
+++ b/scripts/docker/buildpack-deps/Dockerfile.ubuntu.clang.ossfuzz
@@ -73,18 +73,18 @@ FROM base AS libraries
 # Boost
 RUN set -ex; \
     cd /usr/src; \
-    wget -q 'https://archives.boost.io/release/1.74.0/source/boost_1_74_0.tar.bz2' -O boost.tar.bz2; \
-    test "$(sha256sum boost.tar.bz2)" = "83bfc1507731a0906e387fc28b7ef5417d591429e51e788417fe9ff025e116b1  boost.tar.bz2" && \
+    wget -q 'https://archives.boost.io/release/1.83.0/source/boost_1_83_0.tar.bz2' -O boost.tar.bz2; \
+    test "$(sha256sum boost.tar.bz2)" = "6478edfe2f3305127cffe8caf73ea0176c53769f4bf1585be237eb30798c3b8e  boost.tar.bz2" && \
     tar -xf boost.tar.bz2; \
     rm boost.tar.bz2; \
-    cd boost_1_74_0; \
-    CXXFLAGS="-stdlib=libc++ -pthread" LDFLAGS="-stdlib=libc++" ./bootstrap.sh --with-toolset=clang --prefix=/usr; \
-    ./b2 toolset=clang cxxflags="-stdlib=libc++ -pthread" linkflags="-stdlib=libc++ -pthread" headers; \
-    ./b2 toolset=clang cxxflags="-stdlib=libc++ -pthread" linkflags="-stdlib=libc++ -pthread" \
+    cd boost_1_83_0; \
+    CXXFLAGS="-pthread" ./bootstrap.sh --with-toolset=clang --prefix=/usr; \
+    ./b2 toolset=clang cxxflags=" -pthread" linkflags="-pthread" headers; \
+    ./b2 toolset=clang cxxflags=" -pthread" linkflags="-pthread" \
         link=static variant=release runtime-link=static \
         system filesystem unit_test_framework program_options \
         install -j $(($(nproc)/2)); \
-    rm -rf /usr/src/boost_1_74_0
+    rm -rf /usr/src/boost_1_83_0

Another fix is to downgrade clang to version 15, like it was done by ossfuzz developers in https://github.com/google/oss-fuzz/pull/11714/files#diff-00e309e72907992784fc9669925d1181e3b5e645017e81e675928d2cc10dd25aR17-R18