RFR: JDK-8031759 Configure should handle overrides of tools better

[Magnus Ihse Bursie]

>> - BASIC_PATH_PROGS(READELF, [readelf greadelf]) seems reversed from 
>> the normal case where "g" version of a tool is preferred if available.
> Ok, I fix that. I noted that too but didn't change it. But I agree 
> that preferring the "g" version seems reasonable. (Given that we trust 
> GNU tools more than anything else :))

Updated webrev with this fix: 
http://cr.openjdk.java.net/~ihse/JDK-8031759-better-overriding-of-tools-in-configure/webrev.04

I think now this is the final version. :-)

/Magnus