util/queue.h: add __offsetof
util/queue.h: add __offsetof

It seems that we need stddef.h and a #define to compile this under linux.

Signed-off-by: Colin McCabe <3142ce8a0bdba4a38073365893e6b74f72d9c512@alumni.cmu.edu>

cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish,cmccabe/redfish