[8u] RFR: JDK-8269468: JDK-8269388 breaks the build on older GCCs

[Andrew Hughes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8269468
Webrev: https://cr.openjdk.java.net/~andrew/openjdk8/8269468/webrev.01/

In trying to promote 8u302-b07, I found the addition of -Werror=format-overflow
broke the build on older GCCs (specifically building on RHEL 7).

The option is fairly new, only introduced in GCC 7:

https://gcc.gnu.org/gcc-7/changes.html

Adding a version conditional similar to others in that file fixes the
build.

A quick review and critical-ack of this would be appreciated so we
can promote 8u302-b07.

Thanks,
-- 
Andrew :)
Pronouns: he / him or they / them
Senior Free Java Software Engineer
OpenJDK Package Owner
Red Hat, Inc. (http://www.redhat.com)

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