Don't update mtime in privatize_symbols_macos.sh

It confuses ninja and we see things like the following:

ninja explain: stored deps info out of date for 'CMakeFiles/conflict-set-object.dir/ConflictSet.cpp.o' (1712275080328387291 vs 1712275080349012981)

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