RFR(S): 8241486: G1/Z give warning when using LoopStripMiningIter and turn off LoopStripMiningIter (0)

[Roland Westrelin]

https://bugs.openjdk.java.net/browse/JDK-8241486
http://cr.openjdk.java.net/~roland/8241486/webrev.00/

Setting LoopStripMiningIter on the command line for a GC that has loop
strip mining implicitly enabled causes a warning to be printed and loop
strip mining to be turned off. As suggested in the bug report, this
change moves the validation of loop strip mining options to "AfterErgo".

Roland.