[PATCH, Makefile.in] refine selftest recipes to restore mingw bootstrap

[Olivier Hainque]

Hello Tamar,

> On Nov 28, 2017, at 11:05 , Tamar Christina <tamar.christina@arm.com> wrote:
> 
> Yeah I choose this fix because /dev/null is converted to "nul" by the
> Cygwin/msys2 runtime. So when invoked On the shell it gets converted
> before GCC sees it.
> 
> Nothing against using nul directly, though I am surprised that there's an
> environment that provides Configure, automake and coreutils which doesn't
> convert /dev/null to nul.

My understanding is that it's not only a property of
the environment in which the tool gets executed, but also of
the tool itself.

For gcc in particular, ISTM it depends on the target for
which you configured.

Our toolchains are configured for x86_64-pc-mingw32

Maybe yours are configured for cygwin, not mingw (are they ?),
and then are linked with cygwin libraries which perform various
transformations.

Olivier