How exactly it does not compile? It works just fine for me
(well, to get rid of warnings a (void (*)(void *)) cast is desirable).
What error messages do you get? What glibc rpm version and release are you using?

I'm using glibc-2.2.2-10 (-devel and -common are also 2.2.2-10).

The following code will not compile:

#include <pthread.h>

main()
{
  pthread_mutex_t threads_mutex;

  pthread_cleanup_push(pthread_mutex_unlock, (void *)&threads_mutex);
  pthread_mutex_lock(&threads_mutex);

  if (1)
    {
      pthread_mutex_unlock(&threads_mutex);
      pthread_cleanup_pop(0);
    }
  else
    {
      pthread_mutex_unlock(&threads_mutex);
      pthread_cleanup_pop(0);
    }
}

It fails with:

test.c: In function `main':
test.c:7: warning: passing arg 2 of `_pthread_cleanup_push' from incompatible po
inter type
test.c:15: parse error before `else'
test.c:18: `_buffer' undeclared (first use in this function)
test.c:18: (Each undeclared identifier is reported only once
test.c:18: for each function it appears in.)
test.c: At top level:
test.c:19: parse error before `}'

I was originally mistaken - it's actually the way pthread_cleanup_push() 
and ..._pop() are written that makes code not compile. From looking at the 
preprocessor output, both the _push() and the _pop() need to be at the same 
level. This is nonsense, as these should be true functions.

These cannot be functions, please read the documentation:
   Matching pairs of `pthread_cleanup_push' and `pthread_cleanup_pop'
must occur in the same function, at the same level of block nesting.
Actually, `pthread_cleanup_push' and `pthread_cleanup_pop' are macros,
and the expansion of `pthread_cleanup_push' introduces an open brace
`{' with the matching closing brace `}' being introduced by the
expansion of the matching `pthread_cleanup_pop'.