Intel encodings for trap.

Use a ud2 instruction which generates an undefined instruction
exception.

cranelift/filetests/isa/intel/binary32.cton

@@ -364,5 +364,5 @@ ebb1:
 
     ; asm: ebb2:
 ebb2:
-    jump ebb1                                   ; bin: eb fd
+    trap                                        ; bin: 0f 0b
 }

cranelift/filetests/isa/intel/binary64.cton

@@ -626,5 +626,5 @@ ebb0:
     ; asm: movl %r10d, %ecx
     [-,%rcx]            v32 = uextend.i64 v13           ; bin: 44 89 d1
 
-    return
+    trap                                                ; bin: 0f 0b
 }

cranelift/filetests/wasm/control.cton

@@ -43,3 +43,8 @@ ebb0(v0: i32):
 ebb1(v2: i32):
     return v2
 }
+
+function %undefined() {
+ebb0:
+    trap
+}