Several errors with clang 19

[thierry-FreeBSD]

FreeBSD -CURRENT adopted clang 19, and this causes several compilation errors for linbox.
A full log is available at https://pkg-status.freebsd.org/beefy18/data/main-amd64-default/pf72088b8f67d_s3d0a0dda3a7/logs/linbox-1.7.0_5.log .
If it gets removed, here are some examples:

libtool: compile:  c++ -DHAVE_CONFIG_H -I. -I../.. -I../.. -isystem /usr/local/include -O2 -Wall -DNDEBUG -UDEBUG -I/usr/local/include -pthread -O2 -pipe -fstack-protector-strong -isystem /usr/local/include -fno-strict-aliasing -isystem /usr/local/include -std=c++14 -MT diophantine-solver.lo -MD -MP -MF .deps/diophantine-solver.Tpo -c diophantine-solver.C  -fPIC -DPIC -o .libs/diophantine-solver.o
In file included from diophantine-solver.C:26:
In file included from ../../linbox/algorithms/diophantine-solver.h:29:
In file included from ../../linbox/algorithms/rational-solver.h:41:
In file included from ../../linbox/solutions/methods.h:26:
In file included from ../../linbox/matrix/dense-matrix.h:85:
In file included from ../../linbox/matrix/densematrix/blas-matrix.h:42:
In file included from ../../linbox/vector/blas-vector.h:47:
../../linbox/vector/blas-subvector.h:121:20: error: no member named 'data' in 'BlasSubvector<_Vector>'
  121 |             _ptr(V.data()+beg), _size(dim), _inc(inc), _field(&V.field()) {}
      |                  ~ ^

Or

In file included from diophantine-solver.C:26:
In file included from ../../linbox/algorithms/diophantine-solver.h:29:
In file included from ../../linbox/algorithms/rational-solver.h:44:
In file included from ../../linbox/blackbox/lambda-sparse.h:29:
In file included from ../../linbox/matrix/sparse-matrix.h:76:
../../linbox/matrix/sparsematrix/sparse-ell-matrix.h:1216:16: error: cannot assign to non-static data member '_ld' with const-qualified type 'const size_t &' (aka 'const unsigned long &')
 1216 |                                 _ld        = iter._ld ;
      |                                 ~~~        ^

Or

In file included from diophantine-solver.C:26:
In file included from ../../linbox/algorithms/diophantine-solver.h:29:
In file included from ../../linbox/algorithms/rational-solver.h:44:
In file included from ../../linbox/blackbox/lambda-sparse.h:29:
In file included from ../../linbox/matrix/sparse-matrix.h:77:
../../linbox/matrix/sparsematrix/sparse-ellr-matrix.h:1108:12: error: no viable overloaded '='
 1108 |                                 _rowid = iter._rowid;
      |                                 ~~~~~~ ^ ~~~~~~~~~~~
/usr/include/c++/v1/vector:546:63: note: candidate function not viable: 'this' argument has type 'const std::vector<size_t>' (aka 'const vector<unsigned long>'), but method is not marked const
  546 |   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(const vector& __x);
      |                                                               ^
/usr/include/c++/v1/vector:554:63: note: candidate function not viable: 'this' argument has type 'const std::vector<size_t>' (aka 'const vector<unsigned long>'), but method is not marked const
  554 |   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(initializer_list<value_type> __il) {
      |                                                               ^
/usr/include/c++/v1/vector:569:63: note: candidate function not viable: 'this' argument has type 'const std::vector<size_t>' (aka 'const vector<unsigned long>'), but method is not marked const
  569 |   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI vector& operator=(vector&& __x)
      |                                                               ^