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

[Tony Varghese via cfe-commits]

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+// Test -mloadtime-comment-vars= IR output for C++ on AIX. Four scenarios
+// are covered, each with its own set of named variables and check prefix:
+//
+//  CHECK     — mangled-name matching: file- and namespace-scope variables
+//              receive !loadtime_comment metadata and are added to
+//              llvm.compiler.used; name-matched static data members are
+//              diagnosed and left unpreserved (still emitted as ordinary
+//              definitions). A second pass (NOEMIT) over the same output
+//              proves that listed variables of non-plain-char element type
+//              (wchar_t, char16_t, char8_t) and of non-character type are
+//              not preserved and not emitted. Their diagnostic is covered
+//              by the Sema tests and silenced here.
+//
+//  STORAGE   — storage-duration filtering: thread_local variables are
+//              diagnosed by Sema and receive no metadata; a function-local
+//              static is diagnosed and receives no metadata.
+//
+//  SPACE/DUP — list-parsing edge cases: a name with a leading space matches
+//              nothing; a duplicate name preserves the variable exactly once.
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tonykuttai wrote:

moved the storage-duration and list-parsing scenarios into `loadtime-comment-vars.c` test. C++ now has only the name-mangled matching runs.

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