Add <sys/cpumask.h>.
Collect and gather all scatter cpumask bits to correct headers. This
cleans up the namespace and simplifies platform handling in asm macros.
The cpumask_t together with its macros is already non MI feature that is
used in userland utilities, libraries, kernel scheduler and syscalls.
It deserves sys/ header. Adjust syscalls.master and rerun sysent.
While there, fix an issue in ports that set POSIX env, but has
implementation of setting thread names through pthread_set_name_np().
UnifiedSplitRaw