sim/arm/Makefile.in fix for non-GNU make

[Michael Elizabeth Chastain]

Ben Harris writes:

> sim/arm/Makefile.in currently uses $< in a non-implicit rule.  This
> doesn't work with non-GNU makes (at least NetBSD's one) since $< isn't set
> for non-implicit rules.

I got curious, so I checked the Single Unix Spec for make:

  http://www.opengroup.org/onlinepubs/007908799/xcu/make.html

It says:

   $<
          In  an  inference  rule,  $<  evaluates  to  the filename whose
          existence  allowed  the  inference  rule  to  be chosen for the
          target.  In  the  .DEFAULT  rule, the $< macro evaluates to the
          current  target  name.  The  $<  macro  is  evaluated  only for
          inference  rules.  For  example, in the .c.a inference rule, $<
          represents the prerequisite .c file.

So I think this is a good patch.

My two cents,

Michael C