[clang] [clang][Modules] Complete the implementation of P2615: Meaningful exports (PR #194201)

[Vlad Serebrennikov via cfe-commits]

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+// RUN: %clang_cc1 -std=c++20 -fexceptions -fcxx-exceptions -pedantic-errors %s -verify
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Endilll wrote:

`-verify-directives` is missing.

https://github.com/llvm/llvm-project/pull/194201