Fix cl_khr_3d_image_writes warning

Author: nyalloc

clang/test/Misc/nvptx.languageOptsOpenCL.cl

@@ -126,6 +126,9 @@
 // #error "Incorrect cl_khr_3d_image_writes define"
 // #endif
 #pragma OPENCL EXTENSION cl_khr_3d_image_writes : enable
+#if (__OPENCL_C_VERSION__ >= 120) && defined TEST_CORE_FEATURES
+// expected-warning@-2{{OpenCL extension 'cl_khr_3d_image_writes' is core feature or supported optional core feature - ignoring}}
+#endif
 
 #ifdef cl_khr_gl_event
 #error "Incorrect cl_khr_gl_event define"