[llvm] Implement support for NSDI DebugFunction opcode. (PR #211760)

[Manuel Carrasco via llvm-commits]

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mgcarrasco wrote:

You're right. However, I checked and the `--implicit-check-not=DebugFunction` would not be enough to guarantee that no DebugFunction appears. It will only validate in between the CHECKs and the EOF.

Even if we were adding a new prefix for the CHECK-NOT, if FileCheck is executed with multiple prefixes it won't enough.

The test is updated so llc is executed once, and FileCheck is invoked twice. 

https://github.com/llvm/llvm-project/pull/211760