gdb: fix build error in unittests/vec-utils-selftests.c

gdb: fix build error in unittests/vec-utils-selftests.c

When building with gcc 9.2.0, I get the following build error:

    In file included from /home/simark/src/binutils-gdb/gdb/unittests/vec-utils-selftests.c:23:
    /home/simark/src/binutils-gdb/gdb/gdbsupport/gdb_vecs.h: In instantiation of ‘T unordered_remove(std::__debug::vector<T>&, typename std::__debug::vector<T>::iterator) [with T = selftests::vector_utils_tests::unordered_remove_tests()::obj; typename std::__debug::vector<T>::iterator = __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<selftests::vector_utils_tests::unordered_remove_tests()::obj*, std::__cxx1998::vector<selftests::vector_utils_tests::unordered_remove_tests()::obj, std::allocator<selftests::vector_utils_tests::unordered_remove_tests()::obj> > >, std::__debug::vector<selftests::vector_utils_tests::unordered_remove_tests()::obj>, std::random_access_iterator_tag>]’:
    /home/simark/src/binutils-gdb/gdb/unittests/vec-utils-selftests.c:53:26:   required from here
    /home/simark/src/binutils-gdb/gdb/gdbsupport/gdb_vecs.h:53:5: error: implicitly-declared ‘selftests::vector_utils_tests::unordered_remove_tests()::obj::obj(const selftests::vector_utils_tests::unordered_remove_tests()::obj&)’ is deprecated [-Werror=deprecated-copy]
       53 |   T removed = std::move (*it);
          |     ^~~~~~~
    /home/simark/src/binutils-gdb/gdb/unittests/vec-utils-selftests.c:41:10: note: because ‘selftests::vector_utils_tests::unordered_remove_tests()::obj’ has user-provided ‘selftests::vector_utils_tests::unordered_remove_tests()::obj& selftests::vector_utils_tests::unordered_remove_tests()::obj::operator=(const selftests::vector_utils_tests::unordered_remove_tests()::obj&)’
       41 |     obj &operator= (const obj &other)
          |          ^~~~~~~~
    In file included from /home/simark/src/binutils-gdb/gdb/unittests/vec-utils-selftests.c:23:
    /home/simark/src/binutils-gdb/gdb/gdbsupport/gdb_vecs.h:58:10: error: implicitly-declared ‘selftests::vector_utils_tests::unordered_remove_tests()::obj::obj(const selftests::vector_utils_tests::unordered_remove_tests()::obj&)’ is deprecated [-Werror=deprecated-copy]
       58 |   return removed;
          |          ^~~~~~~
    /home/simark/src/binutils-gdb/gdb/unittests/vec-utils-selftests.c:41:10: note: because ‘selftests::vector_utils_tests::unordered_remove_tests()::obj’ has user-provided ‘selftests::vector_utils_tests::unordered_remove_tests()::obj& selftests::vector_utils_tests::unordered_remove_tests()::obj::operator=(const selftests::vector_utils_tests::unordered_remove_tests()::obj&)’
       41 |     obj &operator= (const obj &other)
          |          ^~~~~~~~

I think gcc is just trying to be nice and recommends the good practice
of providing a copy constructor if an assignment operator is provided.

Silence the warning by providing that copy constructor.

gdb/ChangeLog:

	* unittests/vec-utils-selftests.c (unordered_remove_tests::obj):
	Provide explicit default and copy constructor.

Change-Id: I323361b1c120bf8525613b74e7e5983910e002df