Fix Linux /sys cpu path to guess number of cores

[viric]

The path was wrong on linux so it always went to the fallback case.

[teleprint-me]

Are you sure about that?

20:16:51 | ~
  λ file /sys/devices/system/cpu    
/sys/devices/system/cpu: directory
20:16:55 | ~
  λ file /sys/devices/system/cpu/cpu 
/sys/devices/system/cpu/cpu: cannot open `/sys/devices/system/cpu/cpu' (No such file or directory)
20:16:58 | ~
  λ ls /sys/devices/system/cpu
amd_pstate  cpu12  cpu3  cpu8           hotplug     nohz_full  present
cpu0        cpu13  cpu4  cpu9           isolated    offline    smt
cpu1        cpu14  cpu5  cpufreq        kernel_max  online     uevent
cpu10       cpu15  cpu6  cpuidle        microcode   possible   vulnerabilities
cpu11       cpu2   cpu7  crash_hotplug  modalias    power

Source: https://www.kernel.org/doc/html/latest/admin-guide/abi-stable.html#file-stable-sysfs-devices-system-cpu

[viric]

Yes, I'm sure. The code uses an integer to compose these paths:
/sys/devices/system/cpu/cpu0/topology/thread_siblings
/sys/devices/system/cpu/cpu1/topology/thread_siblings
/sys/devices/system/cpu/cpu2/topology/thread_siblings
....

I wrote the change because my computer has 6 cores and llama.cpp used only 3 of them.