Use PRE_LINK

According to
https://cmake.org/cmake/help/latest/command/add_custom_command.html this
more accurately matches the intent

CMakeLists.txt

@@ -128,7 +128,7 @@ endif()
 if(APPLE)
   add_custom_command(
     TARGET ${PROJECT_NAME}-static
-    PRE_BUILD
+    PRE_LINK
     COMMAND ${CMAKE_SOURCE_DIR}/privatize_symbols_macos.sh
             $<TARGET_OBJECTS:${PROJECT_NAME}-object>)
 else()

privatize_symbols_macos.sh

@@ -2,5 +2,7 @@
 
 # This has the effect of making visibility=hidden symbols private in object files
 for obj in "$@" ; do
-  ld -r "$obj" -o "$obj.tmp" && mv "$obj.tmp" "$obj"
+  ld -r "$obj" -o "$obj.tmp"
+  touch -r "$obj" "$obj.tmp"
+  mv "$obj.tmp" "$obj"
 done