6604422: G1: re-use half-promoted regions 6728271: G1: Cleanup G1CollectedHeap::get_gc_alloc_regions() Summary: It allows the last half-full region to be allocated to during a GC to be reused during the next GC. Reviewed-by: apetrusenko, jcoomes

;
; This .DEF file is a placeholder for one which is automatically
; generated during the build process. See
; make\windows\build_vm_def.sh and
; make\windows\makefiles\makedeps.make (esp. the "-prelink"
; options).
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