Fix fibers gdb utils script
Fix fibers gdb utils script

Summary:
There was a recent change in boost compatibility that changed fibers internals and thus broke this script.
This diff fixes gdb script to properly print stack trace for fibers.

Reviewed By: yfeldblum

Differential Revision: D4214575

fbshipit-source-id: 4bf69e9b297c7539a2b2b71093998c30d6a2d81c

floxard/folly,rklabs/folly,rklabs/folly,facebook/folly,Orvid/folly,rklabs/folly,charsyam/folly,rklabs/folly,charsyam/folly,Orvid/folly,facebook/folly,floxard/folly,Orvid/folly,floxard/folly,Orvid/folly,facebook/folly,floxard/folly,floxard/folly,Orvid/folly,charsyam/folly,charsyam/folly,facebook/folly,facebook/folly,rklabs/folly