RFR: 8164485: Zero forms not properly generated

[Claes Redestad]

Hi,

the generation of zero forms in JDK-8164451 was incorrect, since we 
currently don't deal with constant placeholders in forms generated by 
the jlink plugin. While the zero constants might be something we can 
special-case, for now I have to back out the pre-generation of the zero 
forms.

webrev: http://cr.openjdk.java.net/~redestad/8164485/webrev.01/
bug: https://bugs.openjdk.java.net/browse/JDK-8164485

This was caught by existing but rather obscure tests.

Thanks!

/Claes