Fix compilation error in radix.h for older compilers
Summary:
gcc5 gives an error like this:
In file included from ../src/test/radix_tests.cpp:5: In file included from ../src/./radix.h:8: In file included from ../src/./rcu.h:10: /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/atomic:185:7: error: exception specification of explicitly defaulted default constructor does not match the calculated one atomic() noexcept = default; ^ ../src/./radix.h:53:31: note: in instantiation of template class 'std::atomic<RadixTree<radix_tests::TestElement<unsigned long> >::RadixElement>' requested here std::atomic<RadixElement> root; ^ ../src/test/radix_tests.cpp:34:18: note: in instantiation of template class 'RadixTree<radix_tests::TestElement<unsigned long> >' requested here RadixTree<E> mytree; ^ ../src/test/radix_tests.cpp:86:5: note: in instantiation of function template specialization 'radix_tests::testInsert<unsigned long>' requested here testInsert<uint64_t>(); ^
https://cplusplus.github.io/LWG/lwg-unresolved.html for extra context on the issue before it was fixed in newer versions of gcc (ctrl+f for atomic() noexcept for the relevant section)
Test Plan:
make check
ninja check
Reviewers: deadalnix, #bitcoin_abc
Reviewed By: deadalnix, #bitcoin_abc
Subscribers: teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2403