cut out a syscall on thread creation in the case where guard size is 0
[musl] / src / thread / x86_64 /
drwxr-xr-x   ..
-rw-r--r-- 433 __set_thread_area.s
-rw-r--r-- 369 __unmapself.s
-rw-r--r-- 1121 clone.s