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/development/interpreters/ruby/bundler-head.nix

@@ -10,7 +10,7 @@ buildRubyGem {
   };
   dontPatchShebangs = true;
   postInstall = ''
-    find $out -type f -perm /0100 | while read f; do
+    find $out -type f -perm -0100 | while read f; do
       substituteInPlace $f \
          --replace "/usr/bin/env" "${coreutils}/bin/env"
     done

pkgs/development/interpreters/ruby/bundler.nix

@@ -6,7 +6,7 @@ buildRubyGem {
   sha256 = "1zkxw6699bbmsamrij2lirscbh0j58p1p3bql22jsxvx34j6w5nc";
   dontPatchShebangs = true;
   postInstall = ''
-    find $out -type f -perm /0100 | while read f; do
+    find $out -type f -perm -0100 | while read f; do
       substituteInPlace $f \
          --replace "/usr/bin/env" "${coreutils}/bin/env"
     done