[SYCL][E2E][Bindless] Fix -Werror issues (#14912)

Consists of two parts:
1. Fix the setting of `-Werror` on Windows in general for E2E tests
* Just appending to `SYCL_E2E_CLANG_CXX_FLAGS` adds an extra semicolon
that causes the command line to fail
3. Address remaining `-Werror` failures in Bindless Images E2E tests
    * Add return from function, even though there's an `assert(false)`

sycl/test-e2e/CMakeLists.txt

@@ -60,7 +60,8 @@ if(MSVC AND NOT SYCL_TEST_E2E_STANDALONE)
 else()
   set(SYCL_E2E_CLANG_CXX_FLAGS ${CMAKE_CXX_FLAGS})
 endif()
-list(APPEND SYCL_E2E_CLANG_CXX_FLAGS "-Werror")
+
+set(SYCL_E2E_CLANG_CXX_FLAGS "${SYCL_E2E_CLANG_CXX_FLAGS} -Werror")
 
 if(SYCL_TEST_E2E_STANDALONE)
   configure_file("${CMAKE_CURRENT_SOURCE_DIR}/lit.site.cfg.py.in"

sycl/test-e2e/bindless_images/helpers/sampling.hpp

@@ -662,6 +662,7 @@ read(sycl::range<2> globalSize, sycl::vec<float, 2> coords, float offset,
     }
   }
   assert(false && "Invalid sampler encountered!");
+  return {};
 }
 
 }; // namespace sampling_helpers