Cater for use of `__errno_r()` in ChibiOS syscalls.c with newer picolibc revisions (#25121)

platforms/chibios/errno.h

@@ -0,0 +1,13 @@
+// Copyright 2025 Nick Brassel (@tzarc)
+// SPDX-License-Identifier: GPL-2.0-or-later
+#pragma once
+#include_next <errno.h>
+
+// Newer versions of picolibc don't seem to provide `__errno_r(r)` in the header file, but is used by ChibiOS.
+#ifndef __errno_r
+#    ifdef __REENT_ERRNO
+#        define __errno_r(r) _REENT_ERRNO(r)
+#    else
+#        define __errno_r(r) (errno)
+#    endif
+#endif