win32: don't run subprocess tests on Mingw32 platform

On Tue, Jun 14, 2016 at 04:44:57PM +0100, Daniel P. Berrange wrote:
> The g_test_trap_subprocess() method does not work on the
> Mingw32 platform, causing the test-qdev-global-props
> test case to abort
>
> (test-logging.exe:230): GLib-ERROR **: g_test_trap_subprocess()
> failed: Failed to execute helper program (No such file or directory)
>
> This failure was introduced a while ago in
>
>   commit 2177801a
>   Author: Eduardo Habkost <ehabkost@redhat.com>
>   Date:   Fri Aug 8 16:03:27 2014 -0300
>
>     test-qdev-global-props: Run tests on subprocess
>
> Modify the configure time check to avoid enabling this feature
> on Mingw, rather than trying to rewrite the test to avoid this
> feature.

I would do the following instead, just in case we have extra code
looking at $glib_subprocess one day.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

configure

@@ -3014,7 +3014,7 @@ fi
 
 # g_test_trap_subprocess added in 2.38. Used by some tests.
 glib_subprocess=yes
-if ! $pkg_config --atleast-version=2.38 glib-2.0; then
+if test "$mingw32" = "yes" || ! $pkg_config --atleast-version=2.38 glib-2.0; then
     glib_subprocess=no
 fi