Getting these errors:-

make[3]: Leaving directory '/home/pi/src/bitcoin-core-v0.21'
/bin/bash ../libtool  --tag=CXX --preserve-dup-deps  --mode=link clang++ -std=c++11 -O0 -g3 -ftrapv -Wstack-protector -fstack-protector-all -Wall -Wextra -Wgnu -Wformat -Wformat-security -Wvla -Wshadow-field -Wswitch -Wthread-safety -Wrange-loop-analysis -Wredundant-decls -Wunused-variable -Wdate-time -Wconditional-uninitialized -Wsign-compare -Woverloaded-virtual -Wunreachable-code-loop-increment -Wno-unused-parameter -Wno-self-assign -Wno-unused-local-typedef -Wno-deprecated-register -Wno-implicit-fallthrough    -fPIE    -Wl,-z,relro -Wl,-z,now -Wl,-z,separate-code -pie     -pthread -lpthread  -o bitcoind bitcoind-bitcoind.o  libbitcoin_server.a libbitcoin_wallet.a libbitcoin_common.a libbitcoin_util.a univalue/libunivalue.la  libbitcoin_consensus.a crypto/libbitcoin_crypto_base.a    leveldb/libleveldb.a crc32c/libcrc32c.a    leveldb/libmemenv.a secp256k1/libsecp256k1.la -L/usr/lib/arm-linux-gnueabihf -lboost_system -lboost_filesystem -lboost_thread -lpthread -ldb_cxx -lminiupnpc -levent_pthreads -levent -levent  -lsqlite3 
libtool: link: clang++ -std=c++11 -O0 -g3 -ftrapv -Wstack-protector -fstack-protector-all -Wall -Wextra -Wgnu -Wformat -Wformat-security -Wvla -Wshadow-field -Wswitch -Wthread-safety -Wrange-loop-analysis -Wredundant-decls -Wunused-variable -Wdate-time -Wconditional-uninitialized -Wsign-compare -Woverloaded-virtual -Wunreachable-code-loop-increment -Wno-unused-parameter -Wno-self-assign -Wno-unused-local-typedef -Wno-deprecated-register -Wno-implicit-fallthrough -fPIE -Wl,-z -Wl,relro -Wl,-z -Wl,now -Wl,-z -Wl,separate-code -pie -pthread -o bitcoind bitcoind-bitcoind.o  -lpthread libbitcoin_server.a libbitcoin_wallet.a libbitcoin_common.a libbitcoin_util.a univalue/.libs/libunivalue.a libbitcoin_consensus.a crypto/libbitcoin_crypto_base.a leveldb/libleveldb.a crc32c/libcrc32c.a leveldb/libmemenv.a secp256k1/.libs/libsecp256k1.a -L/usr/lib/arm-linux-gnueabihf -lboost_system -lboost_filesystem -lboost_thread -lpthread -ldb_cxx -lminiupnpc -levent_pthreads -levent -levent /usr/lib/arm-linux-gnueabihf/libsqlite3.so -pthread
/usr/bin/ld: bitcoind-bitcoind.o: in function `std::chrono::duration<long long, std::ratio<1ll, 1000000ll> > std::chrono::__duration_cast_impl<std::chrono::duration<long long, std::ratio<1ll, 1000000ll> >, std::ratio<1000ll, 1ll>, long long, false, true>::__cast<long long, std::ratio<1ll, 1000ll> >(std::chrono::duration<long long, std::ratio<1ll, 1000ll> > const&)':
/usr/bin/../lib/gcc/arm-linux-gnueabihf/8/../../../../include/c++/8/chrono:168: undefined reference to `__mulodi4'
/usr/bin/ld: libbitcoin_server.a(libbitcoin_server_a-init.o): in function `AppInitParameterInteraction(ArgsManager const&)':
/home/pi/src/bitcoin-core-v0.21/src/init.cpp:1102: undefined reference to `__mulodi4'
/usr/bin/ld: /home/pi/src/bitcoin-core-v0.21/src/init.cpp:1103: undefined reference to `__mulodi4'
/usr/bin/ld: /home/pi/src/bitcoin-core-v0.21/src/init.cpp:1103: undefined reference to `__mulodi4'
/usr/bin/ld: libbitcoin_server.a(libbitcoin_server_a-init.o): in function `AppInitMain(util::Ref const&, NodeContext&, interfaces::BlockAndHeaderTipInfo*)':
/home/pi/src/bitcoin-core-v0.21/src/init.cpp:1532: undefined reference to `__mulodi4'
/usr/bin/ld: libbitcoin_server.a(libbitcoin_server_a-init.o):/home/pi/src/bitcoin-core-v0.21/src/init.cpp:1532: more undefined references to `__mulodi4' follow
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [Makefile:8343: bitcoind] Error 1
make[2]: Leaving directory '/home/pi/src/bitcoin-core-v0.21/src'
make[1]: *** [Makefile:19347: all-recursive] Error 1
make[1]: Leaving directory '/home/pi/src/bitcoin-core-v0.21/src'
make: *** [Makefile:801: all-recursive] Error 1

Seems similar to this issue, so I'm assuming it has something to do with the choice to use clang - https://github.com/android/ndk/issues/506

{
    const T i = fuzzed_data_provider.ConsumeIntegral<T>();
    const T j = fuzzed_data_provider.ConsumeIntegral<T>();
    const bool is_multiplication_overflow_custom = MultiplicationOverflow(i, j);
#if defined(HAVE_BUILTIN_MUL_OVERFLOW)
    T result_builtin;
    const bool is_multiplication_overflow_builtin = __builtin_mul_overflow(i, j, &result_builtin);
    assert(is_multiplication_overflow_custom == is_multiplication_overflow_builtin);
    if (!is_multiplication_overflow_custom) {
        assert(i * j == result_builtin);
    }
#else
    if (!is_multiplication_overflow_custom) {
        (void)(i * j);
    }
#endif
}
} 
FUZZ_TARGET(multiplication_overflow)