Recent change broke bfin-elf

[Jeff Law]

This change:

> commit 66dfedc28778e81d9d75a4a3fa1e74192138bf62
> Author: Mike Frysinger <vapier@gentoo.org>
> Date:   Wed Feb 2 01:06:21 2022 -0500
>
>     libgloss: merge bfin into top-level Makefile
>
>     Avoid a recursive make to speed things up a bit.

Broke the bfin-elf port with:

../../../../..//newlib-cygwin/libgloss/bfin/basiccrt.S:28:10: fatal 
error: sys/platform.h: No such file or directory
    28 | #include <sys/platform.h>