Prepare DECL/DEAD construction with location

Add new constructors to code_{decl,dead}t that also take a location.
This will help avoid some *_nonconst() calls. To facilitate this,
an additional make_dead instruction builder is also needed (which just
mirrors what we already have for other instruction types).

Author: tautschnig

src/goto-programs/goto_instruction_code.h

@@ -129,6 +129,11 @@ class code_deadt : public codet
   {
   }
 
+  code_deadt(symbol_exprt symbol, source_locationt loc)
+    : codet(ID_dead, {std::move(symbol)}, std::move(loc))
+  {
+  }
+
   symbol_exprt &symbol()
   {
     return static_cast<symbol_exprt &>(op0());
@@ -201,6 +206,11 @@ class code_declt : public codet
   {
   }
 
+  code_declt(symbol_exprt symbol, source_locationt loc)
+    : codet(ID_decl, {std::move(symbol)}, std::move(loc))
+  {
+  }
+
   symbol_exprt &symbol()
   {
     return static_cast<symbol_exprt &>(op0());

src/goto-programs/goto_program.h

@@ -929,13 +929,27 @@ class goto_programt
     return instructiont(_code, l, OTHER, nil_exprt(), {});
   }
 
+  static instructiont make_decl(
+    const code_declt &_code,
+    const source_locationt &l = source_locationt::nil())
+  {
+    return instructiont(_code, l, DECL, nil_exprt(), {});
+  }
+
   static instructiont make_decl(
     const symbol_exprt &symbol,
     const source_locationt &l = source_locationt::nil())
   {
     return instructiont(code_declt(symbol), l, DECL, nil_exprt(), {});
   }
 
+  static instructiont make_dead(
+    const code_deadt &_code,
+    const source_locationt &l = source_locationt::nil())
+  {
+    return instructiont(_code, l, DEAD, nil_exprt(), {});
+  }
+
   static instructiont make_dead(
     const symbol_exprt &symbol,
     const source_locationt &l = source_locationt::nil())
@@ -1047,13 +1061,6 @@ class goto_programt
       code_assignt(std::move(lhs), std::move(rhs)), l, ASSIGN, nil_exprt(), {});
   }
 
-  static instructiont make_decl(
-    const code_declt &_code,
-    const source_locationt &l = source_locationt::nil())
-  {
-    return instructiont(_code, l, DECL, nil_exprt(), {});
-  }
-
   /// Create a function call instruction
   static instructiont make_function_call(
     const code_function_callt &_code,