xz: Use relative paths in pkg-config metadata file

By default, the liblzma pkg-config file (liblzma.pc) is generated with
absolute paths, which $(STAGING_DIR_HOST)/bin/pkg-config is unable to
override.

This patches the file to use paths relative to ${prefix} and
${exec_prefix}.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

utils/xz/Makefile

@@ -10,7 +10,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=xz
 PKG_VERSION:=5.2.4
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=@SF/lzmautils