[8u] RFR: JDK-8139813: Base heap size on type of boot jdk, not architecture of build machine

[Erik Joelsson]

Hello,

Please review this minor configure fix. The logic in configure for 
setting up proper mx flags for the bootjdk is flawed in that it assumes 
a 64bit bootjdk if the build machine is 64bit. This patch fixes this by 
instead testing if the bootjdk is 64bit or not. The problem was 
discovered in 8u and is causing trouble for certain build setups there. 
Since it also applies to 9, I'm posting a webrev for each, intending to 
fix this in both releases.

Bug: https://bugs.openjdk.java.net/browse/JDK-8139813
Webrev JDK 9: http://cr.openjdk.java.net/~erikj/8139813/webrev.jdk9.01/
Webrev JDK 8u: http://cr.openjdk.java.net/~erikj/8139813/webrev.jdk8u.01/

/Erik