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/patches/001-relative-pkg-config-paths.patch

@@ -0,0 +1,13 @@
+--- a/src/liblzma/liblzma.pc.in
++++ b/src/liblzma/liblzma.pc.in
+@@ -7,8 +7,8 @@
+ 
+ prefix=@prefix@
+ exec_prefix=@exec_prefix@
+-libdir=@libdir@
+-includedir=@includedir@
++libdir=${exec_prefix}/lib
++includedir=${prefix}/include
+ 
+ Name: liblzma
+ Description: General purpose data compression library