[llvm] [AMDGPU] Add target feature for waits before system scope stores. NFC. (PR #164993)

[Petar Avramovic via llvm-commits]

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@@ -1,22 +1,50 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
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petar-avramovic wrote:

Think waits are optimized out in final output of ll test, proper test where waits are inserted is mir version of the same test llvm/test/CodeGen/AMDGPU/wait-before-stores-with-scope_sys.mir
Iirc test shows how to generate scope:SCOPE_SYS, options are volatile store or intinsic with argument that corresponds to the bitmask for scope

https://github.com/llvm/llvm-project/pull/164993