[clang] [Clang] diagnosing missing Vulkan environment when using SPIR-V triple (PR #190840)

[Tony Guillot via cfe-commits]

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to268 wrote:

```suggestion
- Fixed an issue where an assert was thrown instead of an error if no vulkan env was specified with ``-target spirv``. (#GH189964)

```

> It would be better to put it at the end of the section instead.

Here, and I have corrected the end of your sentence.

https://github.com/llvm/llvm-project/pull/190840