threads: Automatically call ssh_init on load

This makes unnecessary to call ssh_init() when the library is
dynamically loaded.  Also removes the threads shared library.  The used
threads implementation is chosen in configuration time, changing the
ssh_threads_get_default() depending on the available threads library.

Internally, it is expected a threads implementation providing:

- void ssh_mutex_lock(void **mutex);
- void ssh_mutex_unlock(void **mutex);
- struct ssh_threads_callbacks_struct *ssh_threads_get_default(void);

and a crypto implementation providing:

- int crypto_thread_init(struct ssh_threads_callbacks_struct *user_callbacks);
- void crypto_thread_finalize(void);

This adds internal threads implementation for pthreads and noop.

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/threads.h

@@ -24,8 +24,33 @@
 #include <libssh/libssh.h>
 #include <libssh/callbacks.h>
 
+#if HAVE_PTHREAD
+
+#include <pthread.h>
+#define SSH_MUTEX pthread_mutex_t
+
+#if defined _GNU_SOURCE
+#define SSH_MUTEX_STATIC_INIT PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP
+#else
+#define SSH_MUTEX_STATIC_INIT PTHREAD_MUTEX_INITIALIZER
+#endif
+
+#else
+
+# define SSH_MUTEX void *
+#define SSH_MUTEX_STATIC_INIT NULL
+
+#endif
+
 int ssh_threads_init(void);
 void ssh_threads_finalize(void);
 const char *ssh_threads_get_type(void);
 
+void ssh_mutex_lock(SSH_MUTEX *mutex);
+void ssh_mutex_unlock(SSH_MUTEX *mutex);
+
+struct ssh_threads_callbacks_struct *ssh_threads_get_default(void);
+int crypto_thread_init(struct ssh_threads_callbacks_struct *user_callbacks);
+void crypto_thread_finalize(void);
+
 #endif /* THREADS_H_ */