tests: disable global props test for old glib

follow-up patch moves global property tests to subprocesses.
Unfortunately with old glib this causes:

tests/test-qdev-global-props.c: In function
‘test_static_prop’:
tests/test-qdev-global-props.c:80:5: error: implicit
declaration of function ‘g_test_trap_subprocess’
[-Werror=implicit-function-declaration]
tests/test-qdev-global-props.c:80:5: error: nested extern
declaration of ‘g_test_trap_subprocess’ [-Werror=nested-externs]

This function was only added in glib 2.38, and our
minimum version is 2.12.

To fix, disable the test for glib < 2.38.

Apply before that patch to avoid breaking bisect.
Reported-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

configure

@@ -2716,6 +2716,12 @@ for i in $glib_modules; do
     fi
 done
 
+# g_test_trap_subprocess added in 2.38. Used by some tests.
+glib_subprocess=yes
+if ! $pkg_config --atleast-version=2.38 glib-2.0; then
+    glib_subprocess=no
+fi
+
 ##########################################
 # SHA command probe for modules
 if test "$modules" = yes; then
@@ -4585,6 +4591,9 @@ if test "$bluez" = "yes" ; then
   echo "CONFIG_BLUEZ=y" >> $config_host_mak
   echo "BLUEZ_CFLAGS=$bluez_cflags" >> $config_host_mak
 fi
+if test "glib_subprocess" = "yes" ; then
+  echo "CONFIG_HAS_GLIB_SUBPROCESS_TESTS=y" >> $config_host_mak
+fi
 echo "GLIB_CFLAGS=$glib_cflags" >> $config_host_mak
 if test "$gtk" = "yes" ; then
   echo "CONFIG_GTK=y" >> $config_host_mak

tests/Makefile

@@ -58,7 +58,7 @@ check-unit-y += tests/test-int128$(EXESUF)
 # all code tested by test-int128 is inside int128.h
 gcov-files-test-int128-y =
 check-unit-y += tests/test-bitops$(EXESUF)
-check-unit-y += tests/test-qdev-global-props$(EXESUF)
+check-unit-$(CONFIG_HAS_GLIB_SUBPROCESS_TESTS) += tests/test-qdev-global-props$(EXESUF)
 check-unit-y += tests/check-qom-interface$(EXESUF)
 gcov-files-check-qom-interface-y = qom/object.c
 check-unit-$(CONFIG_POSIX) += tests/test-vmstate$(EXESUF)