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>

src/CMakeLists.txt

@@ -167,9 +167,23 @@ set(libssh_SRCS
   chachapoly.c
 )
 
+if (CMAKE_USE_PTHREADS_INIT)
+    set(libssh_SRCS
+        ${libssh_SRCS}
+        threads/noop.c
+        threads/pthread.c
+    )
+else()
+    set(libssh_SRCS
+        ${libssh_SRCS}
+        threads/noop.c
+    )
+endif()
+
 if (WITH_GCRYPT)
     set(libssh_SRCS
         ${libssh_SRCS}
+        threads/libgcrypt.c
         libgcrypt.c
         gcrypt_missing.c
         pki_gcrypt.c
@@ -178,6 +192,7 @@ if (WITH_GCRYPT)
 elseif (WITH_MBEDTLS)
     set(libssh_SRCS
         ${libssh_SRCS}
+        threads/mbedtls.c
         libmbedcrypto.c
         mbedcrypto_missing.c
         pki_mbedcrypto.c
@@ -186,6 +201,7 @@ elseif (WITH_MBEDTLS)
 else (WITH_GCRYPT)
     set(libssh_SRCS
         ${libssh_SRCS}
+        threads/libcrypto.c
         pki_crypto.c
         ecdh_crypto.c
         libcrypto.c
@@ -319,6 +335,3 @@ if (WITH_STATIC_LIB)
 endif (WITH_STATIC_LIB)
 
 message(STATUS "Threads_FOUND=${Threads_FOUND}")
-if (Threads_FOUND)
-    add_subdirectory(threads)
-endif (Threads_FOUND)