[SYCL] Update image accessor constructor (#5312)

Changed image_accessor() constructor from "= default" to user defined to make it possible to use const references in parallel_for.

Author: IgorKharchikov

sycl/include/CL/sycl/accessor.hpp

@@ -494,7 +494,7 @@ class image_accessor
 
 #ifdef __SYCL_DEVICE_ONLY__
   // Default constructor for objects later initialized with __init member.
-  image_accessor() = default;
+  image_accessor() : MImageObj() {}
 #endif
 
   // Available only when: accessTarget == access::target::host_image

sycl/test/check_device_code/const_ref_image_accessor.cpp

@@ -0,0 +1,11 @@
+// RUN: %clangxx -fsycl -fsycl-device-only -fsyntax-only -Xclang -verify -Xclang -verify-ignore-unexpected=note,warning %s
+
+// expected-no-diagnostics
+
+#include <sycl/sycl.hpp>
+
+SYCL_EXTERNAL void func() {
+  const sycl::accessor<sycl::float4, 2, sycl::access::mode::read,
+                       sycl::access::target::image>
+      x;
+}