[analyzer] Invalidate the region passed to pthread_setspecific() call.

Make this call an exception in ExprEngine::invalidateArguments:
'int pthread_setspecific(ptheread_key k, const void *)' stores
a value into thread local storage. The value can later be retrieved
with 'void *ptheread_getspecific(pthread_key)'. So even thought the
parameter is 'const void *', the region escapes through the
call.

(Here we just blacklist the call in the ExprEngine's default
logic. Another option would be to add a checker which evaluates
the call and triggers the call to invalidate regions.)

Teach the Malloc Checker, which treats all system calls as safe about
the API.

llvm-svn: 151220