[GHC] #8517: Add library function retrieve label set by GHC.Conc.Sync.labelThread

[GHC]

#8517: Add library function retrieve label set by GHC.Conc.Sync.labelThread
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       Reporter:  blitzcode         |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  libraries/base    |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 It would be useful to be able to retrieve the label set by the labelThread
 function. For instance, a logging / tracing system could output a human
 readable string for the thread the trace originated from instead of just
 the thread ID.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8517>
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