RFR: JDK-8210988 Improved handling of compiler warnings in the build

Thu Sep 20 23:41:00 UTC 2018

This is the first part towards a better framework in the build for 
handling compiler warnings. The basic idea is that we should have 
consistent way for all compilers to:

1) enable all (relevant) warnings

2) disable individual warnings, on a global scale (if 1 enables too much)

In particular, this means unifying the basic set of enabled warnings 
between hotspot and the JDK native libraries.

 From that starting point, warnings can be disabled on a per-library 
fashion, if it does not make sense for that specific library. (Like how 
it's done today, but more consistently performed.)

This first part will just put most of the infrastructure in place, and 
strives to keep exactly the same warnings enabled or disabled for all code.

Bug: https://bugs.openjdk.java.net/browse/JDK-8210988
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8210988-improved-warning-flags-handling/webrev.01

/Magnus