[PATCH] 8151841: Build needs additional flags to compile with GCC 6

[Andrew Hughes]

Webrevs:
  http://cr.openjdk.java.net/~andrew/openjdk7/8151841/hotspot/
  http://cr.openjdk.java.net/~andrew/openjdk7/8151841/jdk/
Bug: https://bugs.openjdk.java.net/browse/JDK-8151841

The OpenJDK build needs some additional flags for building with GCC 6.
These have been added in OpenJDK 9 [0] and have been proposed for
OpenJDK 8u [1].

The 7 webrev has the same end result, but is different in content
due to the different build systems. The 7 version is much simpler
because there is no ability to check for the support of flags
without autoconf. So, we add -std=gnu++98 to all invocations of
the C++ compiler, and -fno-lifetime-dse and
-fno-delete-null-pointer-checks if running on GCC >= 6.

Let me know if this is ok to push.

[0] http://hg.openjdk.java.net/jdk9/dev/rev/9d77f922d694
[1] http://mail.openjdk.java.net/pipermail/jdk8u-dev/2016-July/005690.html
-- 
Andrew :)

Senior Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

PGP Key: ed25519/35964222 (hkp://keys.gnupg.net)
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