[clang] [llvm] [AMDGPU] Adding the amdgpu-num-work-groups function attribute (PR #79035)

[Matt Arsenault via cfe-commits]

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@@ -137,6 +137,12 @@ Removed Compiler Flags
 
 Attribute Changes in Clang
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+- Introduced a new function attribute ``__attribute__((amdgpu_max_num_work_groups(x, y, z)))`` or
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arsenm wrote:

Ugh. The ISA manuals usually use "workgroup". read_work_group_size came from OpenCL. We made up amdgpu_flat_work_group_size 

https://github.com/llvm/llvm-project/pull/79035