Prepare XtraDB to be used with xtrabackup.

The changes are deliberately kept minimal

- some functions are made global instead of static (they will be used in
xtrabackup later on)

- functions got additional parameter, deliberately unused for now :
  fil_load_single_tablespaces
  srv_undo_tablespaces_init

- Global variables added, also unused for now :
   srv_archive_recovery
   srv_archive_recovery_limit_lsn
   srv_apply_log_only
   srv_backup_mode
   srv_close_files

- To make xtrabackup link with sql.lib on Windows, added some missing
  source files to sql.lib

- Fixed os_thread_ret_t to be DWORD on Windows

sql/CMakeLists.txt

@@ -77,6 +77,12 @@ IF(SSL_DEFINES)
  ADD_DEFINITIONS(${SSL_DEFINES})
 ENDIF()
 
+IF(WIN32)
+  SET(NT_SERVICE_SOURCES nt_servc.cc nt_servc.h )
+ELSE()
+  SET(NT_SERVICE_SOURCES)
+ENDIF()
+
 SET (SQL_SOURCE
               ../sql-common/client.c compat56.cc derror.cc des_key_file.cc
                discover.cc ../libmysql/errmsg.c field.cc  field_conv.cc 
@@ -143,6 +149,7 @@ SET (SQL_SOURCE
                ${GEN_SOURCES}
                ${GEN_DIGEST_SOURCES}
                ${MYSYS_LIBWRAP_SOURCE}
+               ${NT_SERVICE_SOURCES}
 			   )
   
 IF (CMAKE_SYSTEM_NAME MATCHES "Linux" OR
@@ -172,7 +179,7 @@ TARGET_LINK_LIBRARIES(sql ${MYSQLD_STATIC_PLUGIN_LIBS}
   ${LIBSYSTEMD})
 
 IF(WIN32)
-  SET(MYSQLD_SOURCE main.cc nt_servc.cc nt_servc.h message.rc)
+  SET(MYSQLD_SOURCE main.cc message.rc)
   TARGET_LINK_LIBRARIES(sql psapi)
 ELSE()
   SET(MYSQLD_SOURCE main.cc ${DTRACE_PROBES_ALL})