standalone.sh/.bat enables GC logs automatically if not enabled. But it doesn't necessarily detect all custom GC log options (if someone enabled gc logging without -verbose:gc). Setting PRESERVE_JAVA_OPTS can prevent manipulation of the JAVA_OPTS by the scripts like that, but it'd be nice if there was an option like PRESERVE_JAVA_OPTS to prevent addition of GC logs specifically.
Verified with EAP 6.4.14.CP.CR1
Released with EAP 6.4.14 on March 14 (ZIPs) and March 22 (RPMs).