RFR: JDK-8243985 Make source generation by generatecharacter reproducible

[Magnus Ihse Bursie]

For no really good reason, the generatecharacter buildtool outputs the 
current time in the generated source. While this has no effect on the 
generated class files, it makes gensrc comparison fail between builds.

Bug: https://bugs.openjdk.java.net/browse/JDK-8243985
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8243985-make-generatecharacter-reproducible/webrev.01

/Magnus