libssh: enforce semicolons when using macros

This enforces the usage of semicolons when using CPP macros. We
currently use semicolons anyway, however this leads to certain warnings
on certain compilers.

Fixes curl#6847
Closes curl#6848

lib/vssh/libssh.c

@@ -549,49 +549,52 @@ static int myssh_is_known(struct Curl_easy *data)
   return rc;
 }
 
-#define MOVE_TO_ERROR_STATE(_r) { \
+#define MOVE_TO_ERROR_STATE(_r) do { \
   state(data, SSH_SESSION_DISCONNECT); \
   sshc->actualcode = _r; \
   rc = SSH_ERROR; \
-  break; \
-}
+} while(0); \
+break
 
-#define MOVE_TO_SFTP_CLOSE_STATE() { \
+#define MOVE_TO_SFTP_CLOSE_STATE() do { \
   state(data, SSH_SFTP_CLOSE); \
   sshc->actualcode = sftp_error_to_CURLE(sftp_get_error(sshc->sftp_session)); \
   rc = SSH_ERROR; \
   break; \
-}
+} while(0)
 
-#define MOVE_TO_LAST_AUTH \
+#define MOVE_TO_LAST_AUTH do { \
   if(sshc->auth_methods & SSH_AUTH_METHOD_PASSWORD) { \
     rc = SSH_OK; \
     state(data, SSH_AUTH_PASS_INIT); \
     break; \
   } \
   else { \
     MOVE_TO_ERROR_STATE(CURLE_LOGIN_DENIED); \
-  }
+  } \
+} while(0)
 
-#define MOVE_TO_TERTIARY_AUTH \
+#define MOVE_TO_TERTIARY_AUTH do { \
   if(sshc->auth_methods & SSH_AUTH_METHOD_INTERACTIVE) { \
     rc = SSH_OK; \
     state(data, SSH_AUTH_KEY_INIT); \
     break; \
   } \
   else { \
     MOVE_TO_LAST_AUTH; \
-  }
+  } \
+} while(0)
 
-#define MOVE_TO_SECONDARY_AUTH \
+#define MOVE_TO_SECONDARY_AUTH do { \
   if(sshc->auth_methods & SSH_AUTH_METHOD_GSSAPI_MIC) { \
     rc = SSH_OK; \
     state(data, SSH_AUTH_GSSAPI); \
     break; \
   } \
   else { \
     MOVE_TO_TERTIARY_AUTH; \
-  }
+  } \
+} while(0)
 
 static
 int myssh_auth_interactive(struct connectdata *conn)