Track regmove instruction during binemit.

Register locations can change throughout an EBB. Make sure the
emit_inst() function considers this when encoding instructions and
update the register diversion tracker.

filetests/isa/riscv/regmove.cton

@@ -0,0 +1,15 @@
+; Test tracking of register moves.
+test binemit
+isa riscv
+
+function %regmoves(i32 link [%x1]) -> i32 link [%x1] {
+ebb0(v9999: i32):
+    [-,%x10]            v1 = iconst.i32 1
+    [-,%x7]             v2 = iadd_imm v1, 1000          ; bin: 3e850393
+                        regmove v1, %x10 -> %x11        ; bin: 00050593
+    [-,%x7]             v3 = iadd_imm v1, 1000          ; bin: 3e858393
+                        regmove v1, %x11 -> %x10        ; bin: 00058513
+    [-,%x7]             v4 = iadd_imm v1, 1000          ; bin: 3e850393
+
+    return v9999
+}