[llvm] [llvm][test] Fix filecheck annotation typos [1.5/n] (PR #94857)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

> Rebased, failing `llvm/test/TableGen/MixedCasedMnemonic.td`, looks like actual output changed from last time.
> 
> Need suggestions how to fix it or simply throw away fix for that test for now.

You can execute the test without piping its output to FileCheck to get the actual output, then copy the relevant piece of it into the test and add check lines.
The actual run line should be in the log, look for something like "running at line" (don't remember exact spelling, but should be easy to figure out).
You can execute this single test like the following:
```
<path/to/build>/bin/llvm-lit -vs <path/to/source>/llvm/test/TableGen/MixedCasedMnemonics.td
```


https://github.com/llvm/llvm-project/pull/94857