build: require yajl >= 2.0.3

The pkg-config file was introduced by commit b729ded which was released
in yajl 2.0.3.

Since all our supported platforms include at least yajl 2.0.4,
use pkg-config to detect the library and set the minimum to 2.0.3.

https://repology.org/project/yajl/versionsSigned-off-by: NJán Tomko <jtomko@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

m4/virt-driver-qemu.m4

@@ -29,7 +29,7 @@ AC_DEFUN([LIBVIRT_DRIVER_CHECK_QEMU], [
   dnl There is no way qemu driver will work without JSON support
   AC_REQUIRE([LIBVIRT_CHECK_YAJL])
   if test "$with_qemu:$with_yajl" = "yes:no"; then
-    AC_MSG_ERROR([YAJL or YAJL2 is required to build QEMU driver])
+    AC_MSG_ERROR([YAJL 2 is required to build QEMU driver])
   fi
   if test "$with_qemu" = "check"; then
     with_qemu=$with_yajl

m4/virt-yajl.m4

@@ -24,10 +24,8 @@ AC_DEFUN([LIBVIRT_ARG_YAJL],[
 AC_DEFUN([LIBVIRT_CHECK_YAJL],[
   dnl YAJL JSON library http://lloyd.github.com/yajl/
 
-  LIBVIRT_CHECK_LIB_ALT([YAJL], [yajl],
-                        [yajl_parse_complete], [yajl/yajl_common.h],
-                        [YAJL2], [yajl],
-                        [yajl_tree_parse], [yajl/yajl_common.h])
+  LIBVIRT_CHECK_PKG([YAJL], [yajl], [2.0.3])
+  AC_DEFINE_UNQUOTED([WITH_YAJL2], 1, [whether YAJL2 is enabled])
 ])
 
 AC_DEFUN([LIBVIRT_RESULT_YAJL],[