configure: Use an explicit CONFIG_IVSHMEM rather than CONFIG_EVENTFD

Rather than relying on everywhere that cares about whether the host
supports ivshmem using CONFIG_EVENTFD, make configure set an explicit
CONFIG_IVSHMEM.

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1500021225-4118-3-git-send-email-peter.maydell@linaro.org
[PMM: split out from another patch, add commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/configure b/configure
index befebe2..dbd1313 100755
--- a/configure
+++ b/configure
@@ -5038,6 +5038,11 @@
 qemu_datadir=$datadir$confsuffix
 qemu_localedir="$datadir/locale"
 
+# We can only support ivshmem if we have eventfd
+if [ "$eventfd" = "yes" ]; then
+  ivshmem=yes
+fi
+
 tools=""
 if test "$want_tools" = "yes" ; then
   tools="qemu-img\$(EXESUF) qemu-io\$(EXESUF) $tools"
@@ -6033,6 +6038,10 @@
   echo "HAVE_UTMPX=y" >> $config_host_mak
 fi
 
+if test "$ivshmem" = "yes" ; then
+  echo "CONFIG_IVSHMEM=y" >> $config_host_mak
+fi
+
 # Hold two types of flag:
 #   CONFIG_THREAD_SETNAME_BYTHREAD  - we've got a way of setting the name on
 #                                     a thread we have a handle to