RFR: 8006288: build-infra: Use solaris nm and not gnm on solaris

[Erik Joelsson]

Small patch changing configure to only look for nm and never gnm on 
Solaris. Gnm is still needed in the compare script and is assigned to a 
new variable GNM.

http://cr.openjdk.java.net/~erikj/8006288/webrev.01/

/Erik