patcht5580: add Cygwin support

> t5580 tests that specifying Windows UNC paths works with Git.  Cygwin
> supports UNC paths, albeit only using forward slashes, not backslashes,
> so run the compatible tests on Cygwin as well as MinGW.
> 
> The only complication is Cygwin's `pwd`, which returns a *nix-style
> path, and that's not suitable for calculating the UNC path to the
> current directory.  Instead use Cygwin's `cygpath` utility to get the
> Windows-style path.

> t5580 tests that specifying Windows UNC paths works with Git.  Cygwin
> supports UNC paths, albeit only using forward slashes, not backslashes,
> so run the compatible tests on Cygwin as well as MinGW.
>
> The only complication is Cygwin's `pwd`, which returns a *nix-style
> path, and that's not suitable for calculating the UNC path to the
> current directory.  Instead use Cygwin's `cygpath` utility to get the
> Windows-style path.
>
> Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
> ---
>  t/t5580-clone-push-unc.sh | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/t/t5580-clone-push-unc.sh b/t/t5580-clone-push-unc.sh
> index b322c2f72..47a9a7cda 100755
> --- a/t/t5580-clone-push-unc.sh
> +++ b/t/t5580-clone-push-unc.sh
> @@ -3,12 +3,16 @@
>  test_description='various Windows-only path tests'
>  . ./test-lib.sh
>  
> -if ! test_have_prereq MINGW; then
> +if test_have_prereq CYGWIN; then
> +	alias winpwd='cygpath -aw .'
> +elif test_have_prereq MINGW; then
> +	alias winpwd=pwd
> +else
>  	skip_all='skipping Windows-only path tests'
>  	test_done
>  fi

>  
> -UNCPATH="$(pwd)"
> +UNCPATH="$(winpwd)"
>  case "$UNCPATH" in
>  [A-Z]:*)
>  	# Use administrative share e.g. \\localhost\C$\git-sdk-64\usr\src\git
> @@ -45,8 +49,8 @@ test_expect_success push '
>  	test "$rev" = "$(git rev-parse --verify refs/heads/to-push)"
>  '
>  
> -test_expect_success 'remote nick cannot contain backslashes' '
> -	BACKSLASHED="$(pwd | tr / \\\\)" &&
> +test_expect_success MINGW 'remote nick cannot contain backslashes' '
> +	BACKSLASHED="$(winpwd | tr / \\\\)" &&
>  	git ls-remote "$BACKSLASHED" >out 2>err &&
>  	test_i18ngrep ! "unable to access" err
>  '

> Adam Dinwoodie <adam@dinwoodie.org> writes:
> 
> > t5580 tests that specifying Windows UNC paths works with Git.  Cygwin
> > supports UNC paths, albeit only using forward slashes, not backslashes,
> > so run the compatible tests on Cygwin as well as MinGW.
> >
> > The only complication is Cygwin's `pwd`, which returns a *nix-style
> > path, and that's not suitable for calculating the UNC path to the
> > current directory.  Instead use Cygwin's `cygpath` utility to get the
> > Windows-style path.
> >
> > Signed-off-by: Adam Dinwoodie <adam@dinwoodie.org>
> > ---
> >  t/t5580-clone-push-unc.sh | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/t/t5580-clone-push-unc.sh b/t/t5580-clone-push-unc.sh
> > index b322c2f72..47a9a7cda 100755
> > --- a/t/t5580-clone-push-unc.sh
> > +++ b/t/t5580-clone-push-unc.sh
> > @@ -3,12 +3,16 @@
> >  test_description='various Windows-only path tests'
> >  . ./test-lib.sh
> >  
> > -if ! test_have_prereq MINGW; then
> > +if test_have_prereq CYGWIN; then
> > +	alias winpwd='cygpath -aw .'
> > +elif test_have_prereq MINGW; then
> > +	alias winpwd=pwd
> > +else
> >  	skip_all='skipping Windows-only path tests'
> >  	test_done
> >  fi
> 
> The fact that UNCPATH matters only on windows-related platforms
> justifies the name used for this alias, I guess ;-)