[C++][Gandiva] Always use gdv_function_stubs.h in context_helper.cc

gdv_function_stubs.h has declarations of functions in
context_helper.cc.

cpp/src/gandiva/context_helper.cc

@@ -15,11 +15,13 @@
 // specific language governing permissions and limitations
 // under the License.
 
+#include "gandiva/execution_context.h"
+#include "gandiva/gdv_function_stubs.h"
+
 // This file is also used in the pre-compiled unit tests, which do include
 // llvm/engine/..
 #ifndef GANDIVA_UNIT_TEST
 #include "gandiva/exported_funcs.h"
-#include "gandiva/gdv_function_stubs.h"
 
 #include "gandiva/engine.h"
 
@@ -56,8 +58,6 @@ arrow::Status ExportedContextFunctions::AddMappings(Engine* engine) const {
 }  // namespace gandiva
 #endif  // !GANDIVA_UNIT_TEST
 
-#include "gandiva/execution_context.h"
-
 extern "C" {
 
 void gdv_fn_context_set_error_msg(int64_t context_ptr, char const* err_msg) {