Core/Build: Handle USE_SCRIPTPCH cmake flag when SCRIPTS flag is set to FALSE

Don't ignore USE_SCRIPTPCH cmake flag if SCRIPTS is set to FALSE; in this case "script" project has only source files related to scripted spells and command scripts and it must be built with precompiled headers if USE_SCRIPTPCH flag is set. This partially reverts 780ed1b01c77ac142e1da5851ff7deb832413b11 .