Make pthread_create report sched_setscheduler failures on LP64.

We couldn't fix this for 32-bit because there's too much broken
code out there. (Pretty much everyone asks for real-time
scheduling for all their threads, and the kernel says "don't be
stupid".)

Change-Id: I43c5271e6b6bb91278b9a19eec08cbf05391e3c4