Request for review(M): 6964776: c2 should ensure the polling page is reachable on 64 bit

[Igor Veresov]

C1 and C2 could only use rip-relative addressing when emitting the 
page-polling code, which limited the distance from the code cache to the 
polling page is more than 2G (doesn't fit in a signed 32bit 
displacement). The solution in this case is to materialize the absolute 
pointer to the polling page in a register first, as we do on SPARC.

Webrev: http://cr.openjdk.java.net/~iveresov/6964776/webrev.00/

Thanks,
igor