RFR (M) 8201537: Remove is_alive closure from Klass::is_loader_alive()

[coleen.phillimore at oracle.com]

Summary: remove is_alive closure from callers of Klass::is_loader_alive 
so that cleaning metadata doesn't require GC closure.

This changes runtime, GC and compiler code.

Tested with mach5 tier1-5 with no failures.

open webrev at http://cr.openjdk.java.net/~coleenp/8201537.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8201537

Thanks,
Coleen