cups: Use pkg-config to find cups backend dir

Some distributions(Gentoo) patch cups backend path to
something else than libdir. Use pkg-config to find backend
path for cups.

Makefile.tools

@@ -538,7 +538,8 @@ endif
 endif
 
 if CUPS
-cupsdir = $(libdir)/cups/backend
+
+cupsdir = $(CUPSDIR)
 
 cups_PROGRAMS = profiles/cups/bluetooth
 

configure.ac

@@ -246,6 +246,9 @@ AC_SUBST(UDEV_DIR, [${path_udevdir}])
 AC_ARG_ENABLE(cups, AS_HELP_STRING([--disable-cups],
                 [disable CUPS printer support]), [enable_cups=${enableval}])
 AM_CONDITIONAL(CUPS, test "${enable_cups}" != "no")
+if (test "${enable_cups}" != "no"); then
+   AC_SUBST(CUPSDIR, `$PKG_CONFIG cups --variable=cups_serverbin`/backend)
+fi
 
 AC_ARG_ENABLE(mesh, AS_HELP_STRING([--enable-mesh],
 		[enable Mesh profile support]), [enable_mesh=${enableval}])