keg_relocate (linux): prepend gcc/lib/current to RPATH when needed

This should help keep bottles that require GCC working when
Homebrew/homebrew-core#106755 is merged.

This only works on freshly-poured bottles. Previously installed bottles
will still break on systems with a host GCC older than GCC 11.

Library/Homebrew/extend/os/linux/keg_relocate.rb

@@ -32,6 +32,7 @@ class Keg
 
       lib_path = "#{new_prefix}/lib"
       rpath << lib_path unless rpath.include? lib_path
+      rpath.prepend HOMEBREW_PREFIX/"opt/gcc/lib/current" if rpath.any? { |rp| rp.match?(%r{lib/gcc/\d+$}) }
 
       rpath.join(":")
     end