Request for reviews (XS): 7104561: UseRDPCForConstantTableBase doesn't work after shorten branches changes

[Christian Thalinger]

http://cr.openjdk.java.net/~twisti/7104561/

7104561: UseRDPCForConstantTableBase doesn't work after shorten branches changes
Reviewed-by:

Before 7063629 Compile::shorten_branches was not used on SPARC.  Now
all architectures call that method and we need to take care of that
fact in MachConstantNode::constant_offset when called from
Compile::scratch_emit_size.