[libclc] [NFC][libclc] Merge atomic extension built-ins with identical name into a single file (PR #134489)

[Fraser Cormack via cfe-commits]

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@@ -6,6 +6,17 @@
 //
 //===----------------------------------------------------------------------===//
 
+// cl_khr_global_int32_base_atomics
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frasercrmck wrote:

Sorry to go back to this but I think really these should all be `#if` guarded with the appropriate extension: `cl_khr_(local|global)_int32_(base|extended)_atomics`. It works now because only targets that should build the atomics builtins are including these headers, which isn't the worst thing but it might be good to fix this up since we're here.

https://github.com/llvm/llvm-project/pull/134489