Ever read gdb output and you just kinda get a headache because you have
to infer what a thread is by reading the stack trace? It's not hard, but
we could also just never have to do that again, which is also not hard.
Sample:
(gdb) info thr
Id Target Id Frame
* 1 LWP 3719283 "nix-daemon" 0x00007e558587da0f in accept ()
from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6
2 LWP 3719284 "signal handler" 0x00007e55857b2bea in sigtimedwait ()
from target:/nix/store/c10zhkbp6jmyh0xc5kd123ga8yy2p4hk-glibc-2.39-52/lib/libc.so.6
The API design for this is forced by the macOS pthread_setname_np only
being able to change the current thread's name, but if we just conform
everything to that, it works everywhere.
Change-Id: I2b1d6ed41e3c94170cb0b4e73ad66f239ebd9c88
