RFR: 8210495: compiler crashes because of illegal signature in otherwise legal code

[Maurizio Cimadamore]

Hi,
this is a fix for the issue described in a recent compiler-dev thread 
[1]; the fix does two things:

1) adds proper catch of illegal signature exceptions in LambdaToMethod
2) Add ability to avoid exception throwing when generating signature for 
those clients that can live with loose semantics

Crucially (2) allows to retain compatibility with previously serialized 
names. If e.g. we required all types to be erased prior to deserialized 
lambda name generation, we would obtain a different hash.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/8210495/

JBS:

https://bugs.openjdk.java.net/browse/JDK-8210495

Maurizio