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

[Jay Foad 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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jayfoad wrote:

@petar-avramovic this test added in #82996 is strange because it never actually showed any waits being inserted.

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