RFR (XS): 8047763: Recognize sparc64 as a sparc platform

[Mikael Vidstedt]

Please review the following change which adds code to recognize 
"sparc64" as a 64-bit sparc platform. sparc64 is what uname returns on 
linux/sparc, and is the value which trickles up to the platform.m4 switch.

(I've excluded the generated-configure.sh scripts in the webrev).

Bug: https://bugs.openjdk.java.net/browse/JDK-8047763
Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8047763/webrev.00/webrev/

Thanks,
Mikae