daltenty wrote:

> Uhm - this looks pretty big and seems like something that can easily break 
> certain build configurations since it doesn't seem to touch only AIX

Agreed that this looks big and scary, but it's a purely mechanical change, that 
is a no-op for most targets. I'll add a long form rational at the end of the 
comment about why I don't think the patch effects anyone but AIX to keep my 
answers brief.

>Is this in main without any issues?

Yes, these patches have been in main for several weeks at this point with no 
reported issues.

>  Does it really NEED to be merged for the release branch at this point?

It would help us out for the point releases. Without this patch, we're unable 
to build on AIX with CMake from our package manager (4.0). We can manually 
downgrade if we're unwilling

**Rationale about why the patch doesn't affect targets besides AIX**

We quote the string AIX and variable expansions which might expand to string 
AIX (i.e. `CMAKE_SYSTEM_NAME`), so that we do the intent string comparison. If 
not quoted the if will expand the string if it happens to match a variable name 
(which `AIX` does in CMake 4.0+).

This has an effect only if `CMAKE_SYSTEM_NAME` 
(https://cmake.org/cmake/help/latest/variable/CMAKE_SYSTEM_NAME.html) expands 
to something which is a CMake variable 
(https://cmake.org/cmake/help/latest/manual/cmake-variables.7.html#variables-that-describe-the-system)

Intersecting the two list gives me the following list of affect targets:
```
AIX
CYGWIN
MSYS
WASI
```

Of those targets, only CYGWIN appears in the lines affected by the patch, and 
it's already using a variable check (i.e. it checks `CYGWIN`) not a string 
comparison to `CMAKE_SYSTEM_NAME`, so it's unaffected.

https://github.com/llvm/llvm-project/pull/156505
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