Move type_traits.h into solvers/smt2_incremental/

Because this is the only part of the codebase where it is currently used
and moving it means the PR with this commit should need fewer code
reviewer approvals.

Author: thomasspriggs

src/solvers/smt2_incremental/smt_terms.h

@@ -4,10 +4,10 @@
 #define CPROVER_SOLVERS_SMT2_INCREMENTAL_SMT_TERMS_H
 
 #include <util/irep.h>
-#include <util/type_traits.h>
 
 #include <solvers/smt2_incremental/smt_index.h>
 #include <solvers/smt2_incremental/smt_sorts.h>
+#include <solvers/smt2_incremental/type_traits.h>
 
 #include <functional>
 #include <utility>

src/util/type_traits.h renamed to src/solvers/smt2_incremental/type_traits.h

@@ -5,8 +5,8 @@
 /// or C++17 to C++11. These can be replaced with the standard library versions
 /// as and when we upgrade the version CBMC is compiled with.
 
-#ifndef CPROVER_UTIL_TYPE_TRAITS_H
-#define CPROVER_UTIL_TYPE_TRAITS_H
+#ifndef CPROVER_SOLVERS_SMT2_INCREMENTAL_TYPE_TRAITS_H
+#define CPROVER_SOLVERS_SMT2_INCREMENTAL_TYPE_TRAITS_H
 
 #include <type_traits>
 
@@ -34,4 +34,4 @@ struct make_voidt
 template <typename... typest>
 using void_t = typename detail::make_voidt<typest...>::type;
 
-#endif // CPROVER_UTIL_TYPE_TRAITS_H
+#endif // CPROVER_SOLVERS_SMT2_INCREMENTAL_TYPE_TRAITS_H