RFR: JDK-8149479: Fix compare.sh to have a clean baseline with COMPARE_BUILD

[Tim Bell]

Erik:

> Please review these fixes for compare.sh and the COMPARE_BUILD flag 
> for make.
>
> The rather new feature COMPARE_BUILD, which builds twice, applying 
> some kind of change between them, is really neat. Especially when run 
> through JPRT to check all platforms at once. The problem is that 
> compare.sh currently isn't clean on all these platforms. There are 
> also some special peculiarities particular to when JPRT is running the 
> build which confuses compare.sh.
>
> Given that COMPARE_BUILD uses the exact same output directory, and 
> JPRT sets the version-opt string to a fix value for both builds, we 
> should be able to achieve a clean and stable baseline for an empty 
> patch file. Which I now have.
>
> I also changed COMPARE_BUILD to fail the build when differences are 
> found and added an option to COMPARE_BUILD to disable failing.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8149479
> Webrev: http://cr.openjdk.java.net/~erikj/8149479/webrev.01/

1) Regarding common/bin/compare.sh lines 336...341 and lines 344...349 
in the new version - this is not directly related to 8149479 but I wish 
those regexes were only coded once.  If they ever get out of sync the 
results will be puzzling.

2) make/InitSupport.gmk line 366 in the new version - typo? 
COMPARE_BUILD_FAILE is COMPARE_BUILD_FAIL elsewhere

Looks good otherwise.

Tim