[9] RFR(S) 8181757: NonNMethod heap in segmented CodeCache is not scanned in some cases

[dean.long at oracle.com]

https://bugs.openjdk.java.net/browse/JDK-8181757

http://cr.openjdk.java.net/~dlong/8181757/webrev/


When I first added FOR_ALL_NMETHOD_HEAPS, I accidentally conflated "code 
heaps that can contain nmethods" and "code heaps that don't contain AOT 
methods", with the difference being the segmented NonNMethod code heap.  
This change fixes that with a new FOR_ALL_ALLOCABLE_HEAPS for non-aot heaps.

This fix is targeted for 9.

dl