Use ordered map for commit log

In general, unordered maps should not be used for iteration, only for
lookups.

In this case, using an ordered map guarantees that the order in which
writes are logged is consistent for a given instruction.

Resolves #1499

riscv/processor.h

@@ -62,7 +62,7 @@ struct insn_desc_t
 };
 
 // regnum, data
-typedef std::unordered_map<reg_t, freg_t> commit_log_reg_t;
+typedef std::map<reg_t, freg_t> commit_log_reg_t;
 
 // addr, value, size
 typedef std::vector<std::tuple<reg_t, uint64_t, uint8_t>> commit_log_mem_t;