Valid arguments are "all", "present", or a comma delimited list of engine names.
The "all" option will try to build against all supported SDKs. (This is the default.)
The "present" option will only attempt to build against SDKs that exist on the system.
Examples:
configure.py --sdks=css,csgo,ep2v
configure.py --sdks=l4d
configure.py -s present