[clang] [llvm] [Clang][AIX] Add -mloadtime-comment-vars flag to preserve identifying variables (PR #187986)

[Hubert Tong via cfe-commits]

================
@@ -6873,6 +6873,100 @@ When ``#pragma comment(copyright, ...)`` appears in a C++20 module interface
 unit, the copyright string is embedded only in the object file compiled from
 that interface unit. Importing TUs do not re-emit the string.
 
+Preserving Identifying Variables with -mloadtime-comment-vars
+--------------------------------------------------------------
+
+The ``-mloadtime-comment-vars=`` flag accepts a comma-separated list of
+global variable names that should be preserved in the final object file as
+loadtime identifying strings. This is an AIX-specific feature; on other
+targets the compiler emits a warning and the flag is not forwarded to
+``-cc1``.
----------------
hubert-reinterpretcast wrote:

Too much implementation detail for user-facing documentation.
```suggestion
targets the compiler emits a warning.
```

https://github.com/llvm/llvm-project/pull/187986