[libc][sched] Fix CPU_SET and CPU_ISSET macros (#194830)
Fix the public CPU_SET and CPU_ISSET macros to match the expected
two-argument forms and to use cpu_set_t instead of the misspelled
cpt_set_t.
Also declare the helper functions used by the CPU set macros in the
generated sched.h header, and add regression coverage for the CPU set
macro family.
