[clang] [llvm] [Utils] Add new --update-tests flag to llvm-lit (PR #108425)

[Nicolai Hähnle via cfe-commits]

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@@ -1,3 +1,5 @@
+// RUN: %clang_cc1 -verify %s
+// RUN: diff %s %s.expected
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nhaehnle wrote:

I still think those new invocations of `diff` should be in `lit-plugin.test`.

Those `diff` lines attempt to check that this file (or rather its temporarily copied version) was overwritten correctly.

It isn't sound to have the code to check whether a file was correctly overwritten in the file that is overwritten.

https://github.com/llvm/llvm-project/pull/108425