JDK-8136771: Implement the license-swap logic as a make target

[Erik Joelsson]

Hello,

This is the open part of a larger Oracle internal change. I've 
reimplemented how the .hgtip files are created. Now these can be 
generated with only open source present. This is nice to have if you 
create a source bundle and want to keep the information about where in 
the HG history that source came from. There is also a minor build bugfix 
in GensrcModuleInfo.gmk for when building with prebuilt crypto binaries.

Bugs: https://bugs.openjdk.java.net/browse/JDK-8136771
Webrev: http://cr.openjdk.java.net/~erikj/8136771/webrev.top.01/