[clang] [llvm] [Clang]: Enable speculative devirtualization (PR #159685)

[Hassnaa Hamdi via llvm-commits]

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+// Test that the vtable metadata that are emitted by Clang when speculative devirtualization
+// is enabled can be used by the WholeProgramDevirt pass without being dropped on the way.
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hassnaaHamdi wrote:

I don't want to test the DropUnnecessaryAssumes pass specifically, because the intrinsics could be dropped by any other pass but I moved it to llvm/test/Transforms/WholeProgramDevirt. Does that make sense ?

https://github.com/llvm/llvm-project/pull/159685