[clang] [clang][analyzer] Move unix.BlockInCriticalSection out of alpha (PR #93815)

[Balazs Benics via cfe-commits]

================
@@ -1235,6 +1235,49 @@ Check calls to various UNIX/Posix functions: ``open, pthread_once, calloc, mallo
 .. literalinclude:: checkers/unix_api_example.c
     :language: c
 
+.. _unix-BlockInCriticalSection:
+
+unix.BlockInCriticalSection (C)
+"""""""""""""""""""""""""""""""""""""
+Check for calls to blocking functions inside a critical section.
+Blocking functions detected by this checker: ``sleep, getc, fgets, read, recv``.
+Critical section handling functions modelled by this checker: ``lock, unlock, pthread_mutex_lock, pthread_mutex_trylock, pthread_mutex_unlock, mtx_lock, mtx_timedlock, mtx_trylock, mtx_unlock, lock_guard, unique_lock``.
+
+.. code-block:: c
+
+ void pthread_lock_example(pthread_mutex_t *m) {
+   pthread_mutex_lock(m); // note: entering critical section here
+   sleep(10); // warn: Call to blocking function 'sleep' inside of critical section
+   pthread_mutex_unlock(m);
+ }
+
+.. code-block:: cpp
+
+ void overlapping_critical_sections(mtx_t *m1, std::mutex &m2) {
+   std::lock_guard lg{m2}; // note: entering critical section here
+   mtx_lock(m1); // note: entering critical section here
+   sleep(10); // warn: Call to blocking function 'sleep' inside of critical section
+   mtx_unlock(m1);
+   sleep(10); // warn: Call to blocking function 'sleep' inside of critical section
+             // still inside of the critical section of the std::lock_guard
----------------
steakhal wrote:

```suggestion
              // still inside of the critical section of the std::lock_guard
```

https://github.com/llvm/llvm-project/pull/93815