6820167: GCALotAtAllSafepoints + FullGCALot(ScavengeALot) options crash JVM Summary: Short-circuit gc-a-lot attempts by non-JavaThreads; SkipGCALot c'tor to elide re-entrant gc-a-lot attempts. Reviewed-by: apetrusenko, jcoomes, jmasa, kamg

^build/
^dist/
^nbproject/private/