Use ha16/lo16 to load or store 1, 2, 8 bytes from labels.

Use ha16/lo16 to load or store 1, 2, 8 bytes from labels.

Add the tokens IND_RL_B, IND_RL_H, IND_RL_H_S, IND_RL_D, along with
the rules to use them.  These rules emit shorter code.  For example,
loading a byte becomes lis, lbz instead of lis, addi, lbz.

While making this, I wrongly set IND_RL_D to size 4.  Then ncg made
infinite recursion in codegen() and stackupto(), until it crashed by
stack overflow.  I correctly set IND_RL_D to size 8, preventing the
crash.