Add incremental-smt2-solver command line option

So that the new interface can be kept separate from the existing one
whilst work is in-progress.

Author: thomasspriggs

src/cbmc/cbmc_parse_options.cpp

@@ -409,6 +409,13 @@ void cbmc_parse_optionst::get_command_line_options(optionst &options)
     options.set_option("smt2", true);
   }
 
+  if(cmdline.isset("incremental-smt2-solver"))
+  {
+    options.set_option(
+      "incremental-smt2-solver", cmdline.get_value("incremental-smt2-solver")),
+      solver_set = true;
+  }
+
   if(cmdline.isset("external-sat-solver"))
   {
     options.set_option(
@@ -1042,6 +1049,9 @@ void cbmc_parse_optionst::help()
     " --yices                      use Yices\n"
     " --z3                         use Z3\n"
     " --refine                     use refinement procedure (experimental)\n"
+    " --incremental-smt2-solver cmd\n"
+    "                              command to invoke external SMT solver for\n"
+    "                              incremental solving (experimental)\n"
     " --external-sat-solver cmd    command to invoke SAT solver process\n"
     HELP_STRING_REFINEMENT_CBMC
     " --outfile filename           output formula to given file\n"

src/cbmc/cbmc_parse_options.h

@@ -57,6 +57,7 @@ class optionst;
   OPT_JSON_INTERFACE \
   "(smt1)(smt2)(fpa)(cvc3)(cvc4)(boolector)(yices)(z3)(mathsat)" \
   "(cprover-smt2)" \
+  "(incremental-smt2-solver):" \
   "(external-sat-solver):" \
   "(no-sat-preprocessor)" \
   "(beautify)" \