[llvm] [SHT_LLVM_BB_ADDR_MAP] Emit callsite offsets in the `SHT_LLVM_BB_ADDR_MAP` section. (PR #146563)

[James Henderson via llvm-commits]

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@@ -405,31 +405,72 @@ This section is emitted with ``-basic-block-address-map`` and will contain
 a BB address map table for every function.
 
 The ``SHT_LLVM_BB_ADDR_MAP`` type provides backward compatibility to allow
-reading older versions of the BB address map generated by older compilers. Each
-function entry starts with a version byte which specifies the encoding version
-to use. The following versioning schemes are currently supported.
+reading older versions of the BB address map generated by older compilers (up to
+two years old). Each function entry starts with a version byte which specifies
+the encoding version to use. This follows by a feature byte which specifies the
----------------
jh7370 wrote:

```suggestion
the encoding version to use. This is followed by a feature byte which specifies the
```

https://github.com/llvm/llvm-project/pull/146563