[clang] clang/AMDGPU: Report some missing OpenCL 2.0 feature macros (PR #160826)

[Matt Arsenault via cfe-commits]

================
@@ -156,10 +159,31 @@
 #pragma OPENCL EXTENSION cl_amd_media_ops2: enable
 
 #if (__OPENCL_C_VERSION__ >= 300)
-#ifndef __opencl_c_generic_address_space
-#error "Missing __opencl_c_generic_address_space define"
-#else
-#error "Incorrect __opencl_c_generic_address_space define"
+  #ifndef __opencl_c_program_scope_global_variables
+    #error "Missing __opencl_c_program_scope_global_variables define"
+  #endif
 #endif
-#pragma OPENCL EXTENSION __opencl_c_generic_address_space: enable
+
+#if (__OPENCL_C_VERSION__ >= 300)
+  #ifdef FLAT_SUPPORT
+    #ifndef __opencl_c_generic_address_space
+      #error "Missing __opencl_c_generic_address_space define"
+    #endif
+  #else
+    #ifdef __opencl_c_generic_address_space
+      #error "Incorrect __opencl_c_atomic_scope_all_devices define"
----------------
arsenm wrote:

```suggestion
      #error "Incorrect __opencl_c_generic_address_space define"
```

https://github.com/llvm/llvm-project/pull/160826