[10] Review request: 8197463: Update libxml2 to version 2.9.7

[Arunprasad Rajkumar]

Hi,

Please review the following fix,

Bug: https://bugs.openjdk.java.net/browse/JDK-8197463

Compressed changeset: http://cr.openjdk.java.net/~arajkumar/8197463/webrev.00/libxml2-2.9.7v3.diff.gz 
Cmake only changes for review: http://cr.openjdk.java.net/~arajkumar/8197463/webrev.00/cmake-changes 

Following are list of changes made as part of this bug:

1. Merged libxml2-2.9.7 changes from https://git.gnome.org/browse/libxml2/tag/?h=v2.9.7 
2. Enabled libxml compilation on Linux and macOS 
3. Enabled libxslt compilation on Linux and macOS

Thanks,
Arun