Re-add creation and installation of the json-c.pc file to the cmake build.

CMakeLists.txt

@@ -250,4 +250,10 @@ install(TARGETS ${PROJECT_NAME}
     ARCHIVE DESTINATION lib
 )
 
+if (UNIX OR MINGW OR CYGWIN)
+	configure_file(json-c.pc.in json-c.pc @ONLY)
+	set(INSTALL_PKGCONFIG_DIR "${CMAKE_INSTALL_PREFIX}/lib/pkgconfig" CACHE PATH "Installation directory for pkgconfig (.pc) files")
+	install(FILES ${CMAKE_BINARY_DIR}/json-c.pc DESTINATION "${INSTALL_PKGCONFIG_DIR}")
+endif ()
+
 install(FILES ${JSON_C_PUBLIC_HEADERS} DESTINATION ${CMAKE_INSTALL_PREFIX}/include/json-c)