[clang] [clang][analyzer] Change default value of checker option in unix.StdCLibraryFunctions. (PR #80457)

[via cfe-commits]

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@@ -1299,10 +1299,21 @@ range of the argument.
 
 **Parameters**
 
-The checker models functions (and emits diagnostics) from the C standard by
-default. The ``ModelPOSIX`` option enables modeling (and emit diagnostics) of
-additional functions that are defined in the POSIX standard. This option is
-disabled by default.
+The ``ModelPOSIX`` option controls if functions from the POSIX standard are
+recognized by the checker. If ``true``, a big amount of POSIX functions is
+modeled according to the
+`POSIX standard`_. This
+includes ranges of parameters and possible return values. Furthermore the
+behavior related to ``errno`` in the POSIX case is often that ``errno`` is set
+only if a function call fails, and it becomes undefined after a successful
+function call.
+If ``false``, functions are modeled according to the C99 language standard.
+This includes far less functions than the POSIX case. It is possible that the
+same functions are modeled differently in the two cases because differences in
+the standards. The C standard specifies less aspects of the functions, for
+example exact ``errno`` behavior is often unspecified (and not modeled by the
+checker).
+Default value of the option is ``true``.
----------------
NagyDonat wrote:

```suggestion
The ``ModelPOSIX`` option controls if functions from the POSIX standard are
recognized by the checker.

With ``ModelPOSIX=true``, lots of POSIX functions are modeled according to the
`POSIX standard`_. This includes ranges of parameters and possible return
values. Furthermore the behavior related to ``errno`` in the POSIX case is
often that ``errno`` is set only if a function call fails, and it becomes
undefined after a successful function call.

With ``ModelPOSIX=false``, this checker follows the C99 language standard and
only models the functions that are described there. It is possible that the
same functions are modeled differently in the two cases because differences in
the standards. The C standard specifies less aspects of the functions, for
example exact ``errno`` behavior is often unspecified (and not modeled by the
checker).

Default value of the option is ``true``.
```


https://github.com/llvm/llvm-project/pull/80457