WIP: Add workaround for instruction that fails to encode

The following is no longer legal in asmjit:

    a.cmp(ARG3, TMP2, a64::uxth(0));

The intention is to produce the following instruction:

    cmp ARG3, TMP2, uxth

Until we find out how to express this with the new asmjit, split the
instruction into two instructions:

    and TMP2, TMP2, 0xffff
    cmp ARG3, TMP2

erts/emulator/beam/jit/arm/instr_fun.cpp

@@ -380,7 +380,8 @@ a64::Gp BeamModuleAssembler::emit_call_fun(bool skip_box_test,
         a.ldp(TMP2, ARG1, arm::Mem(TMP2));
 
         /* Combined fun type and arity test. */
-        a.cmp(ARG3, TMP2, a64::uxth(0));
+        a.and_(TMP2, TMP2, imm(0xffff));
+        a.cmp(ARG3, TMP2);
         a.b_ne(next);
     }