bug#38492: 27.0.50; Warn pdumper users when pure space has been overflowed

[Stefan Monnier]

> With portable dumping.  I think pure space provides no benefit.

AFAICT, the purespace provides the same benefit with portable dumping as
it does with unexec.  The benefit is to save time during the GC by not
traversing the purespace.  It's basically an "old" generation in a kind
of very restricted form of generational GC.

Maybe purespace is too small compared to typical heap sizes to make
a significant difference, nowadays.


        Stefan