constify symex_bmct::record_coverage

This member is never written to and serves merely as a cache for a
front-end option, so this commit makes it const.

Author: karkhaz

src/cbmc/bmc.h

@@ -86,8 +86,6 @@ class bmct:public safety_checkert
       ui_message_handler(_message_handler),
       driver_callback_after_symex(callback_after_symex)
   {
-    symex.record_coverage=
-      !options.get_option("symex-coverage-report").empty();
   }
 
   virtual resultt run(const goto_functionst &goto_functions)
@@ -159,8 +157,6 @@ class bmct:public safety_checkert
       ui_message_handler(_message_handler),
       driver_callback_after_symex(callback_after_symex)
   {
-    symex.record_coverage =
-      !options.get_option("symex-coverage-report").empty();
     INVARIANT(
       options.get_bool_option("paths"),
       "Should only use saved equation & goto_state constructor "

src/cbmc/symex_bmc.cpp

@@ -25,7 +25,7 @@ symex_bmct::symex_bmct(
   const optionst &options,
   path_storaget &path_storage)
   : goto_symext(mh, outer_symbol_table, _target, options, path_storage),
-    record_coverage(false),
+    record_coverage(!options.get_option("symex-coverage-report").empty()),
     symex_coverage(ns)
 {
 }

src/cbmc/symex_bmc.h

@@ -80,7 +80,7 @@ class symex_bmct: public goto_symext
     return symex_coverage.generate_report(goto_functions, path);
   }
 
-  bool record_coverage;
+  const bool record_coverage;
 
   unwindsett unwindset;