cleanup: prune old build logs

Closes Homebrew/homebrew#29231.

Library/Homebrew/cmd/cleanup.rb

@@ -10,6 +10,7 @@ module Homebrew extend self
     if ARGV.named.empty?
       cleanup_cellar
       cleanup_cache
+      cleanup_logs
       unless ARGV.dry_run?
         cleanup_lockfiles
         rm_DS_Store
@@ -19,6 +20,20 @@ module Homebrew extend self
     end
   end
 
+  def cleanup_logs
+    time = Time.now - 2 * 7 * 24 * 60 * 60 # two weeks
+    HOMEBREW_LOGS.subdirs.each do |dir|
+      if dir.mtime < time
+        if ARGV.dry_run?
+          puts "Would remove: #{dir}"
+        else
+          puts "Removing: #{dir}..."
+          dir.rmtree
+        end
+      end
+    end
+  end
+
   def cleanup_cellar
     HOMEBREW_CELLAR.subdirs.each do |rack|
       begin