8201370: GC specific data is referred from common precompiled headers and defNewGeneration.cpp Reviewed-by: stefank, shade, dholmes Contributed-by: boris.ulasevich@bell-sw.com

8200233: Simple G1 evacuation path performance enhancements Summary: Implement some minor performance optimizations in the evacuation path including changing some stores to be OOP_NOT_NULL, specializing the compressed/uncompressed oops path and delay some load of the current heapregion until absolutely necessary. Reviewed-by: kbarrett, sjohanss