the flags would have to be protected by platform / target features.

src/sat/smt/arith_axioms.cpp
g++ -o z3 shell/dimacs_frontend.o shell/z3_log_frontend.o shell/install_tactic.o shell/mem_initializer.o shell/datalog_frontend.o shell/gparams_register_modules.o shell/opt_frontend.o shell/smtlib_frontend.o shell/main.o shell/drat_frontend.o api/api.a cmd_context/extra_cmds/extra_cmds.a opt/opt.a tactic/portfolio/portfolio.a tactic/fpa/fpa_tactics.a tactic/ufbv/ufbv_tactic.a tactic/smtlogics/smtlogic_tactics.a muz/fp/fp.a muz/bmc/bmc.a muz/ddnf/ddnf.a muz/tab/tab.a muz/clp/clp.a muz/spacer/spacer.a muz/rel/rel.a muz/transforms/transforms.a muz/dataflow/dataflow.a muz/base/muz.a tactic/fd_solver/fd_solver.a sat/sat_solver/sat_solver.a qe/qe.a tactic/sls/sls_tactic.a smt/tactic/smt_tactic.a tactic/bv/bv_tactics.a nlsat/tactic/nlsat_tactic.a sat/tactic/sat_tactic.a sat/smt/sat_smt.a smt/smt.a smt/proto_model/proto_model.a math/subpaving/tactic/subpaving_tactic.a solver/assertions/solver_assertions.a tactic/arith/arith_tactics.a tactic/core/core_tactics.a ast/fpa/fpa.a ackermannization/ackermannization.a tactic/aig/aig_tactic.a ast/pattern/pattern.a parsers/smt2/smt2parser.a cmd_context/cmd_context.a solver/solver.a qe/lite/qe_lite.a qe/mbp/mbp.a tactic/tactic.a ast/sls/ast_sls.a ast/simplifiers/simplifiers.a ast/converters/converters.a model/model.a ast/macros/macros.a ast/proofs/proofs.a ast/substitution/substitution.a ast/normal_forms/normal_forms.a ast/rewriter/bit_blaster/bit_blaster.a ast/rewriter/rewriter.a math/lp/lp.a nlsat/nlsat.a sat/sat.a math/grobner/grobner.a ast/euf/euf.a parsers/util/parser_util.a smt/params/smt_params.a ast/ast.a math/subpaving/subpaving.a math/realclosure/realclosure.a params/params.a math/automata/automata.a math/hilbert/hilbert.a math/simplex/simplex.a math/dd/dd.a math/interval/interval.a math/polynomial/polynomial.a util/util.a -lpthread
g++ -o libz3.dylib -dynamiclib api/dll/install_tactic.o api/dll/mem_initializer.o api/dll/gparams_register_modules.o api/dll/dll.o api/api_array.o api/api_fpa.o api/api_arith.o api/api_datatype.o api/z3_replayer.o api/api_model.o api/api_log_macros.o api/api_ast_map.o api/api_datalog.o api/api_ast_vector.o api/api_commands.o api/api_opt.o api/api_special_relations.o api/api_algebraic.o api/api_tactic.o api/api_ast.o api/api_context.o api/api_qe.o api/api_log.o api/api_pb.o api/api_polynomial.o api/api_goal.o api/api_rcf.o api/api_seq.o api/api_bv.o api/api_stats.o api/api_config_params.o api/api_solver.o api/api_quant.o api/api_params.o api/api_numeral.o api/api_parsers.o cmd_context/extra_cmds/extra_cmds.a opt/opt.a tactic/portfolio/portfolio.a tactic/fpa/fpa_tactics.a tactic/ufbv/ufbv_tactic.a tactic/smtlogics/smtlogic_tactics.a muz/fp/fp.a muz/bmc/bmc.a muz/ddnf/ddnf.a muz/tab/tab.a muz/clp/clp.a muz/spacer/spacer.a muz/rel/rel.a muz/transforms/transforms.a muz/dataflow/dataflow.a muz/base/muz.a tactic/fd_solver/fd_solver.a sat/sat_solver/sat_solver.a qe/qe.a tactic/sls/sls_tactic.a smt/tactic/smt_tactic.a tactic/bv/bv_tactics.a nlsat/tactic/nlsat_tactic.a sat/tactic/sat_tactic.a sat/smt/sat_smt.a smt/smt.a smt/proto_model/proto_model.a math/subpaving/tactic/subpaving_tactic.a solver/assertions/solver_assertions.a tactic/arith/arith_tactics.a tactic/core/core_tactics.a ast/fpa/fpa.a ackermannization/ackermannization.a tactic/aig/aig_tactic.a ast/pattern/pattern.a parsers/smt2/smt2parser.a cmd_context/cmd_context.a solver/solver.a qe/lite/qe_lite.a qe/mbp/mbp.a tactic/tactic.a ast/sls/ast_sls.a ast/simplifiers/simplifiers.a ast/converters/converters.a model/model.a ast/macros/macros.a ast/proofs/proofs.a ast/substitution/substitution.a ast/normal_forms/normal_forms.a ast/rewriter/bit_blaster/bit_blaster.a ast/rewriter/rewriter.a math/lp/lp.a nlsat/nlsat.a sat/sat.a math/grobner/grobner.a ast/euf/euf.a parsers/util/parser_util.a smt/params/smt_params.a ast/ast.a math/subpaving/subpaving.a math/realclosure/realclosure.a params/params.a math/automata/automata.a math/hilbert/hilbert.a math/simplex/simplex.a math/dd/dd.a math/interval/interval.a math/polynomial/polynomial.a util/util.a -lpthread -Wl,-soname,libz3.so.0
ld: unknown option: -soname

the flags would have to be protected by platform / target features.

So what is the best way to fix the flag missing problem mentioned in issue #7225 ?

Use an if statement that limits the change to the platforms where the change works.

For example, if GMP is enabled then the GMP variable is set to True and SLIBEXTRAFLAGS are updated using -lgmp

    if GMP:
        test_gmp(CXX)
        ARITH = "gmp"
        CPPFLAGS = '%s -D_MP_GMP' % CPPFLAGS
        LDFLAGS  = '%s -lgmp' % LDFLAGS
        SLIBEXTRAFLAGS = '%s -lgmp' % SLIBEXTRAFLAGS
    else:
        CPPFLAGS = '%s -D_MP_INTERNAL' % CPPFLAGS

Got it, thanks.