xerces: bump version, use .tar.xz, add hash file

This commit bumps the version of xerces to 3.1.2, changes tarball to
.tar.xz, and adds a hash file.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/xerces/xerces.hash

@@ -0,0 +1,2 @@
+# From http://www.apache.org/dist/xerces/c/3/sources/xerces-c-3.1.2.tar.xz.sha256
+sha256 a847529ab6125f36039f54fa61f3d5043791accf7da2f43917cd2b49deb768f1 xerces-c-3.1.2.tar.xz

package/xerces/xerces.mk

@@ -4,8 +4,8 @@
 #
 ################################################################################
 
-XERCES_VERSION = 3.1.1
-XERCES_SOURCE = xerces-c-$(XERCES_VERSION).tar.gz
+XERCES_VERSION = 3.1.2
+XERCES_SOURCE = xerces-c-$(XERCES_VERSION).tar.xz
 XERCES_SITE = http://archive.apache.org/dist/xerces/c/3/sources
 XERCES_LICENSE = Apache-2.0
 XERCES_LICENSE_FILES = LICENSE