RFR (XXS): 8004319: test/gc/7168848/HumongousAlloc.java fails after 7172640

[Christian Thalinger]

http://cr.openjdk.java.net/~twisti/8004319

8004319: test/gc/7168848/HumongousAlloc.java fails after 7172640
Reviewed-by:

The problem are root compiles which need to be intrinsified.
Currently there is only one method that has this property:
java.lang.ref.Reference.get()

The fix is to detect root compiles in LibraryCallKit::LibraryCallKit
and set _reexecute_sp to sp().

src/share/vm/opto/library_call.cpp