Libs.private should contain a list of libraries the library that the package
exposes is linked too. So let's filter out unrelated link flags.

diff --git sane-backends-1.1.1/tools/sane-backends.pc.in~ sane-backends-1.1.1/tools/sane-backends.pc.in
index b4d9731f82..dd8adfd89c 100644
--- sane-backends-1.1.1/tools/sane-backends.pc.in~
+++ sane-backends-1.1.1/tools/sane-backends.pc.in
@@ -10,5 +10,5 @@ Description: Backends for SANE, the universal scanner interface
 Version: @VERSION@
 Requires:
 Libs: -L${libdir} -lsane
-Libs.private: ${ldflags} ${libs}
+Libs.private: ${libs}
 Cflags: -I${includedir}