Add target_link_directory() compat function

We need this function to deal with pkgconfig files properly, but
unfortunately it doesn't exist until CMake 3.13, and we need to support
CMake 3.10. So add a hacky compatibility function for older systems.

CMakeLists.txt

@@ -17,6 +17,8 @@ include(CheckCSourceRuns)
 
 include(CMakeMacroLibtoolFile)
 
+include(cmake/TargetLinkDirectories.cmake)
+
 project(tigervnc)
 set(VERSION 1.12.80)
 

cmake/TargetLinkDirectories.cmake

@@ -0,0 +1,12 @@
+# Compatibility replacement of target_link_directories() for older cmake
+
+if(${CMAKE_VERSION} VERSION_LESS "3.13.0")
+  function(target_link_directories TARGET SCOPE)
+    get_target_property(INTERFACE_LINK_LIBRARIES ${TARGET} INTERFACE_LINK_LIBRARIES)
+    foreach(DIRECTORY ${ARGN})
+      list(INSERT INTERFACE_LINK_LIBRARIES 0 "-L${DIRECTORY}")
+    endforeach()
+    set_target_properties(${TARGET} PROPERTIES
+      INTERFACE_LINK_LIBRARIES "${INTERFACE_LINK_LIBRARIES}")
+  endfunction()
+endif()