win32: work around problem with stderr in MSVCRT

Try to run a non-existent command with standard error closed:

   xyz 2>&-

In recent versions of busybox-w32 this resulted in problems with
moving through history (either using up/down keys or ctrl-r) and
tab completion.  In all cases the order of the prompt and the
command were reversed.

Bisection showed the problem was first seen in PRE-5396 which
merged some commits from upstream, including fd47f0567 (lineedit:
print prompt and editing operations to stderr).

This (eventually) called to mind a previous problem with stderr
in xargs which was fixed by commit f192e6539 (xargs: fix 'xargs
-sNUM' tests).  In both cases it seemed that mixing calls to
bb_putchar_stderr() and fprintf(stderr, ...) was at fault.  The
former uses a file descriptor while the latter uses a stream.  It
was almost as if the stream was buffered.

- The problem with xargs affected 32-bit and 64-bit builds with
  MSVCRT.

- The problem with '2>&-' only affected 32-bit builds with MSVCRT.

- Neither problem was present with UCRT builds.

As a workaround change bb_putchar_stderr() to use the stderr stream
in builds for MSVCRT.

Saves 16 bytes in the 32-bit build.

(GitHub issue #460)

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