configure: Suppress messages from pkg_config probe for check

Suppress confusing messages from pkg_config when probing for
'check' by sending them to /dev/null as we do with other
similar probes.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -1828,7 +1828,7 @@ if test "$check_utests" != "no" ; then
 #include <check.h>
 int main(void) { suite_create("qemu test"); return 0; }
 EOF
-  check_libs=`$pkg_config --libs check`
+  check_libs=`$pkg_config --libs check 2>/dev/null`
   if compile_prog "" $check_libs ; then
     check_utests=yes
     libs_tools="$check_libs $libs_tools"