Update linuxthreads.cc

line 196: signum_t doesn't work with 64bit, or multithreaded, or something??, changed to signum.

Error message: 

src/base/linuxthreads.cc: In function 'void ListerThread(ListerParams*)':
src/base/linuxthreads.cc:312:24: error: invalid conversion from 'void (*)(int, siginfo_t*, void*)' to 'void (*)(int, siginfo*, void*)' [-fpermissive]