Enforce complete libssh2 1.9 builds

Treat missing agent and session-timeout symbols as configuration errors once the libssh2 1.9 header floor has been accepted. This prevents header and library mismatches from silently producing a reduced SSH2 API.\n\nName the missing library or symbol in each error so failed builds point directly to the mismatched dependency.

Author: binaryfire

config.m4

@@ -1067,23 +1067,23 @@ EOF
             PHP_ADD_LIBRARY_WITH_PATH(ssh2, $SSH2_DIR/lib, SWOOLE_SHARED_LIBADD)
             AC_DEFINE(SW_HAVE_SSH2LIB, 1, [Have libssh2])
         ],[
-            AC_MSG_ERROR([libssh2 version >= 1.9.0 not found])
+            AC_MSG_ERROR([libssh2 library not found or too old; version 1.9.0 or newer is required])
         ],[
             -L$SSH2_DIR/lib -lm
         ])
 
         PHP_CHECK_LIBRARY(ssh2, libssh2_agent_init, [
             AC_DEFINE(PHP_SSH2_AGENT_AUTH, 1, [Have libssh2 with ssh-agent support])
         ],[
-            AC_MSG_WARN([libssh2 <= 1.2.3, ssh-agent subsystem support not enabled])
+            AC_MSG_ERROR([libssh2_agent_init not found; ensure the linked libssh2 matches the 1.9.0 or newer headers])
         ],[
             -L$SSH2_DIR/lib -lm
         ])
 
         PHP_CHECK_LIBRARY(ssh2, libssh2_session_set_timeout, [
             AC_DEFINE(PHP_SSH2_SESSION_TIMEOUT, 1, [Have libssh2 with session timeout support])
         ],[
-            AC_MSG_WARN([libssh2 < 1.2.9, session timeout support not enabled])
+            AC_MSG_ERROR([libssh2_session_set_timeout not found; ensure the linked libssh2 matches the 1.9.0 or newer headers])
         ],[
             -L$SSH2_DIR/lib -lm
         ])