RFR(s): 8181319: Make os::Linux::sched_getcpu() available even when UseNUMA is false

[Per Liden]

Hi,

The initialization/availability of os::Linux::sched_getcpu() is today 
guarded by UseNUMA. While NUMA-related code is currently the only user 
of sched_getcpu(), this function is useful in many other situations as 
well. I propose that we initialize os::Linux::sched_getcpu() regardless 
of whether UseNUMA is enabled or not.

Bug: https://bugs.openjdk.java.net/browse/JDK-8181319
Webrev: http://cr.openjdk.java.net/~pliden/8181319/webrev.0/
Testing: JPRT, ad-hoc runs using ParallelGC with and without UseNUMA

cheers,
Per