qemu-ga: check if utmpx.h is available on the system

Commit 161a56a9065 added command guest-get-users and requires the
utmpx.h (defined by POSIX) to work. It is however not always available
(e.g. on OpenBSD) therefor a check for its existence is necessary.

Signed-off-by: Tomáš Golembiovský <tgolembi@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
diff --git a/configure b/configure
index a3f0522..e8798ce 100755
--- a/configure
+++ b/configure
@@ -4915,6 +4915,21 @@
 fi
 
 ##########################################
+# check for utmpx.h, it is missing e.g. on OpenBSD
+
+have_utmpx=no
+cat > $TMPC << EOF
+#include <utmpx.h>
+struct utmpx user_info;
+int main(void) {
+    return 0;
+}
+EOF
+if compile_prog "" "" ; then
+    have_utmpx=yes
+fi
+
+##########################################
 # End of CC checks
 # After here, no more $cc or $ld runs
 
@@ -5959,6 +5974,10 @@
   echo "CONFIG_STATIC_ASSERT=y" >> $config_host_mak
 fi
 
+if test "$have_utmpx" = "yes" ; then
+  echo "HAVE_UTMPX=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