[clang] [AMDGPU][Clang] Support for type inferring extended image builtins for AMDGPU (PR #164358)

[Rana Pratap Reddy via cfe-commits]

================
@@ -3,7 +3,7 @@
 
 typedef int int4 __attribute__((ext_vector_type(4)));
 typedef float float4 __attribute__((ext_vector_type(4)));
-typedef half half4 __attribute__((ext_vector_type(4)));
+typedef _Float16 half4 __attribute__((ext_vector_type(4)));
----------------
ranapratap55 wrote:

I was trying to modify the same "x" like below instead of adding new one. 
```
  case 'x':
    assert(HowLong == 0 && !Signed && !Unsigned &&
           "Bad modifiers used with 'x'!");
    Type = Type = Context.getLangOpts().OpenCL ? Context.HalfTy : Context.Float16Ty;
```
with these we don't need to add any new alphabet. I think this would be ideal. what do you suggest? @jmmartinez 

https://github.com/llvm/llvm-project/pull/164358