Add ibranch test.

src/ibranch.gdb

@@ -0,0 +1,2 @@
+c
+info registers r0 r1 r2 r3

src/ibranch.log

@@ -0,0 +1,9 @@
+Breakpoint 1 at 0x10078
+Breakpoint 2 at 0x100c8
+0x0000000000010078 in _start ()
+
+Breakpoint 2, 0x00000000000100c8 in _stop ()
+r0                            <00> 0x0	0
+r1                            <00> 0x1	1
+r2                            <00> 0x2	2
+r3                            <00> 0x3	3

src/ibranch.s

@@ -0,0 +1,30 @@
+.global _start
+.global _stop
+
+_start:
+{
+    ibranch 3f
+}
+0:
+{
+    addd %r0, 1, %r1
+    ibranch 2f
+}
+1:
+{
+    addd %r2, 1, %r3
+    ibranch _stop
+}
+2:
+{
+    addd %r1, 1, %r2
+    ibranch 1b
+}
+3:
+{
+    addd 0, 0, %r0
+    ibranch 0b
+}
+
+_stop:
+    udivs 0, 0, %empty