pypy: fix site-packages linkage

Fixes Homebrew/homebrew#48530.

Formula/pypy.rb

@@ -87,6 +87,12 @@ class Pypy < Formula
     prefix_site_packages.mkpath
 
     # Symlink the prefix site-packages into the cellar.
+    if !(libexec/"site-packages").symlink?
+      # fix the case where libexec/site-packages/site-packages was installed
+      rm_rf libexec/"site-packages/site-packages"
+      mv Dir[libexec/"site-packages/*"], prefix_site_packages
+      rm_rf libexec/"site-packages"
+    end
     libexec.install_symlink prefix_site_packages
 
     # Tell distutils-based installers where to put scripts