libdpkg: Add @LIBLZMA_LIBS@ to Libs.Private in libdpkg.pc.in

If a project is using libdpkg's compression support it will fail to
build with newer libdpkg versions that added direct liblzma support,
because the dependency is an implementation detail, the library could
be using the command line tool instead, and it would not really be
correct for that project to explicitly link against liblzma.

debian/changelog

@@ -3,6 +3,7 @@ dpkg (1.16.10) UNRELEASED; urgency=low
   [ Guillem Jover ]
   * Fix typos in 1.16.9 changelog entry. Closes: #691954
     Thanks to Nicolás Alvarez <nicolas.alvarez@gmail.com>.
+  * Add missing @LIBLZMA_LIBS@ to Libs.Private in libdpkg.pc.in.
 
   [ Updated programs translations ]
   * Esperanto (Felipe Castro).

lib/dpkg/libdpkg.pc.in

@@ -8,5 +8,5 @@ Name: libdpkg
 Description: Debian package management system library
 Version: @VERSION@
 Libs: -L${libdir} -ldpkg
-Libs.private: @ZLIB_LIBS@ @BZ2_LIBS@
+Libs.private: @ZLIB_LIBS@ @LIBLZMA_LIBS@ @BZ2_LIBS@
 Cflags: -I${includedir}