compile warning in ipc_stress on Windows

[gdamore]

C:\projects\nanomsg\tests\ipc_stress.c(104) : warning C4101: 'bytes' : unreferenced local variable
C:\projects\nanomsg\tests\ipc_stress.c(103) : warning C4101: 'cli_sock' : unreferenced local variable
[ 73%] Linking C executable ipc_stress.exe
[ 73%] Built target ipc_stress