threadstruct: remove extra semicolon
threadstruct: remove extra semicolon

Another clang warning-turned-error:

  CXX   source/leakcheck.o
  In file included from source/leakcheck.cpp:24:
  In file included from include/leakcheck.hh:40:
  include/threadstruct.hh:82:29: error: extra ';' inside a struct [-Werror,-Wextra-semi]
    pthread_cond_t * condwait;;
                                ^

plasma-umass/DoubleTake,bpowers/DoubleTake,bpowers/DoubleTake,bpowers/DoubleTake,plasma-umass/DoubleTake,plasma-umass/DoubleTake,bpowers/DoubleTake,bpowers/DoubleTake,bpowers/DoubleTake,plasma-umass/DoubleTake,plasma-umass/DoubleTake,plasma-umass/DoubleTake,plasma-umass/DoubleTake,bpowers/DoubleTake,bpowers/DoubleTake