Compilation fails with clang-16: error: ISO C++17 does not allow 'register' storage class specifier

[yurivict]

In file included from common/nroots-polynomial.cpp:11:
In file included from ../../include/mps/mps.h:66:
../../include/mps/mpc.h:114:37: error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
void mpc_pow_si (mpc_t rc, mpc_t c, register signed long int i);
                                    ^~~~~~~~~

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