fdo#68849: Add header guards to all include files

Added header guards to files in directories stoc/, and svtools/

Change-Id: Ib6691b0e3fa09d71696ab947d357e489eb35df66
Reviewed-on: https://gerrit.libreoffice.org/9584
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>