[8u] RFR 8141491: Unaligned memory access in Bits.c

[David Buck]

Hi!

May I please get a review of this straightforward backport from JDK 9 to 
JDK 8:

bug report:
https://bugs.openjdk.java.net/browse/JDK-8141491

JDK 9 change sets:
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/75f6573e9c44
http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/13759d57abca

JDK 9 review thread:
http://mail.openjdk.java.net/pipermail/nio-dev/2015-November/003365.html
http://mail.openjdk.java.net/pipermail/nio-dev/2016-January/003496.html
http://mail.openjdk.java.net/pipermail/nio-dev/2016-February/003522.html

JDK 8 webrevs (for review):
http://cr.openjdk.java.net/~dbuck/8141491_jdk8_ver00/

The backport is almost line-for-line the same as the JDK 9 fix with the 
following exceptions:

- assertions / guarantees need to have their format strings wrapped with 
err_msg() [0]

- there is no need to "backout" of JDK-8140630 [1], which was never 
backported to JDK 8 in the first place.

This fix is urgently needed for JDK 8 built with newer versions of GCC.

Cheers,
-Buck

[0] https://bugs.openjdk.java.net/browse/JDK-8080775
[1] https://bugs.openjdk.java.net/browse/JDK-8140630