Request for approval: 8210423: Backport of 8034788 breaks GCC version detection

[Andrew Haley]

The JDK8u backport of 8034788 changed the variable name CXX_VERSION
(in configure) to CXX_VERSION_NUMBER. Unfortunately this was not done
consistently, and as a result the version number check for GCC is
broken. As a result of that brokenness, HotSpot built on all GCC
versions >=6 is unstable.

Intriguingly, the comments aroud te affected code are correct, and
refer to CXX_VERSION_NUMBER, but the actual variable name is wrong.

http://cr.openjdk.java.net/~aph/8210423/

OK?

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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