MDEV-9564 - added s390x to lib64 INSTALL_LIBDIR handling

Adjusted INSTALL_LIBDIR detection so that it is set to "lib64" on any 64bit system (not only x86_64). New condition is insipired by GNUInstallDirs cmake module.

Author: svoj

cmake/install_layout.cmake

@@ -137,7 +137,7 @@ SET(INSTALL_SCRIPTDIR_RPM "bin")
 SET(INSTALL_SYSCONFDIR_RPM"/etc")
 SET(INSTALL_SYSCONF2DIR_RPM "/etc/my.cnf.d")
 #
-IF(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64")
+IF(CMAKE_SIZEOF_VOID_P EQUAL 8)
  SET(INSTALL_LIBDIR_RPM "lib64")
  SET(INSTALL_PLUGINDIR_RPM "lib64/mysql/plugin")
 ELSE()