MDEV-22053: Pass INSTALL_LAYOUT "DEB" correctly to CONC (libmariadb)

As this was missing, the libmariadb/install.cmake section for Debian
builds was not triggered at all, and existing fixes to make the
Debian paths correct did not apply.

Update libmariadb3 paths in Debian packaging after MariaDB Connector C
3.1.8 upgrade

Also now include caching_sha2_password.so which was previously omitted.

Keep old libmariadbclient.a as symbolic link for backwards compatibility.

Closes: CONC-304
Related: CONC-456, MDEV-22150

cmake/mariadb_connector_c.cmake

@@ -24,6 +24,8 @@ SET(CONC_WITH_MYSQLCOMPAT ON)
 
 IF (INSTALL_LAYOUT STREQUAL "RPM")
   SET(CONC_INSTALL_LAYOUT "RPM")
+ELSEIF (INSTALL_LAYOUT STREQUAL "DEB")
+  SET(CONC_INSTALL_LAYOUT "DEB")
 ELSE()
   SET(CONC_INSTALL_LAYOUT "DEFAULT")
 ENDIF()

debian/libmariadb-dev.install

 usr/bin/mariadb_config
 usr/include/mariadb
+usr/lib/*/libmariadb.a
 usr/lib/*/libmariadb.so
 usr/lib/*/libmariadbclient.a
 usr/lib/*/libmariadbclient.so

debian/libmariadb3.install

 usr/lib/*/libmariadb.so.*
-usr/lib/mysql/plugin/client_ed25519.so
-usr/lib/mysql/plugin/dialog.so
-usr/lib/mysql/plugin/mysql_clear_password.so
-usr/lib/mysql/plugin/sha256_password.so
+usr/lib/*/libmariadb3/plugin/caching_sha2_password.so
+usr/lib/*/libmariadb3/plugin/client_ed25519.so
+usr/lib/*/libmariadb3/plugin/dialog.so
+usr/lib/*/libmariadb3/plugin/mysql_clear_password.so
+usr/lib/*/libmariadb3/plugin/sha256_password.so

debian/mariadb-plugin-gssapi-client.install

-usr/lib/mysql/plugin/auth_gssapi_client.so
+usr/lib/*/libmariadb3/plugin/auth_gssapi_client.so

debian/rules

@@ -143,6 +143,9 @@ endif
 	ln -s libmariadb.so.3 $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmysqlclient.so.19
 	ln -s libmariadb.so.3 $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmysqlclient.so.20
 
+	# Install libmariadbclient.a compatibility link
+	ln -s libmariadb.a $(TMP)/usr/lib/$(DEB_HOST_MULTIARCH)/libmariadbclient.a
+
 override_dh_fixperms:
 	dh_fixperms
 	chmod 04755 debian/mariadb-server-10.5/usr/lib/mysql/plugin/auth_pam_tool_dir/auth_pam_tool