Fix linking problems with system CPR

The variable we used was not defined when using a system CPR. Instead of defining the variable, we can use the already-defined alias target which also works with a downloaded CPR.

Author: TheAssassin

src/updateinformation/CMakeLists.txt

@@ -20,5 +20,5 @@ target_include_directories(updateinformation
 target_link_libraries(updateinformation
     PRIVATE util
     PRIVATE nlohmann_json::nlohmann_json
-    PRIVATE ${CPR_LIBRARIES}
+    PRIVATE cpr
 )

src/updater/CMakeLists.txt

@@ -12,7 +12,7 @@ set_target_properties(libappimageupdate
 # link thread libraries
 target_link_libraries(libappimageupdate
     PRIVATE ${CMAKE_THREAD_LIBS_INIT}
-    PRIVATE ${CPR_LIBRARIES}
+    PRIVATE cpr
     PRIVATE util
     PRIVATE updateinformation
     PRIVATE signing
@@ -41,7 +41,7 @@ set_target_properties(libappimageupdate_static
 # link thread libraries
 target_link_libraries(libappimageupdate_static
     PRIVATE ${CMAKE_THREAD_LIBS_INIT}
-    PRIVATE ${CPR_LIBRARIES}
+    PRIVATE cpr
     PRIVATE util
     PRIVATE updateinformation
     PRIVATE signing