[Bug go/56431] -lpthread should be added to -lgo

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56431
Bug 56431 depends on bug 56353, which changed state.

Bug 56353 Summary: libgcj should be listed on command line for 
libjava.jni/invocation/PR16923.c
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56353

           What    |Removed                     |Added
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             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WONTFIX