Add rpath to pkg-config file on *BSD.

Reduces diff between configure and CMake builds of libzip.pc.

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index fa9763c..705c61e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -131,10 +131,13 @@
 SET(exec_prefix \${prefix})
 SET(libdir \${exec_prefix}/lib)
 SET(includedir \${prefix}/include)
-SET(LIBS -lz)
 IF(BZIP2_FOUND)
   SET(LIBS "${LIBS} -lbz2")
 ENDIF()
+SET(LIBS "${LIBS} -lz")
+IF(CMAKE_SYSTEM_NAME MATCHES BSD)
+  SET(PKG_CONFIG_RPATH "-Wl,-R\${libdir}")
+ENDif(CMAKE_SYSTEM_NAME MATCHES BSD)
 CONFIGURE_FILE(libzip.pc.in libzip.pc @ONLY)
 INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/libzip.pc DESTINATION lib/pkgconfig)