According to the pkg-config manpage, the "Libs" line in a .pc file
should give the link flags "specific to your package", and specifically
says not to include link flags for dependencies:
Libs: This line should give the link flags specific to your
package. Don't add any flags for required packages;
pkg-config will add those automatically.
Version: @PACKAGE_VERSION@
Requires: libcrypto libssl @PC_LIBEVENT_DEPENDENCY@
Requires.private: @PC_PY_DEPENDENCY@
-Libs: -L${libdir} -lunbound -lssl -lcrypto
+Libs: -L${libdir} -lunbound
Libs.private: @SSLLIB@ @LIBS@
-Cflags: -I${includedir}
+Cflags: -I${includedir}