Compilation warnings

[LeventErkok]

Fresh build warnings, on a Mac:

../src/math/simplex/model_based_opt.h:85:16: warning: class member cannot be redeclared [-Wredeclared-class-member]
   85 |         struct const_def;
      |                ^
../src/math/simplex/model_based_opt.h:83:16: note: previous declaration is here
   83 |         struct const_def;
      |                ^
../src/ast/sls/sls_smt_solver.cpp:103:19: warning: 'rlimit' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
  103 |         reslimit& rlimit() { return m_ddfw.rlimit(); }
      |                   ^
../src/ast/sls/sls_context.h:88:27: note: overridden virtual function is here
   88 |         virtual reslimit& rlimit() = 0;
      |                           ^