mass rewrite of find parameters to cross-platform style

Fixes #9044, close #9667. Thanks to @taku0 for suggesting this solution.
Now we have no modes starting with `/` or `+`.

Rewrite the `-perm` parameters of find:
 - completely safe: rewrite `/0100` and `+100` to `-0100`,
 - slightly semantics-changing: rewrite `+111` to `-0100`.
I cross-verified the `find` manual pages for Linux, Darwin, FreeBSD.

pkgs/servers/plex/default.nix

@@ -31,7 +31,7 @@ stdenv.mkDerivation rec {
       patchelf --set-rpath "$out/usr/lib/plexmediaserver" "$out/usr/lib/plexmediaserver/$bin"
     done
 
-    find $out/usr/lib/plexmediaserver/Resources -type f -a -perm /0100 \
+    find $out/usr/lib/plexmediaserver/Resources -type f -a -perm -0100 \
         -print -exec patchelf --set-interpreter "${glibc}/lib/ld-linux-x86-64.so.2" '{}' \;