* compile.c: Use rb_fstring() to de-duplicate string literals in code.  [ruby-core:58599] [Bug #9159] [ruby-core:54405]
* iseq.c (prepare_iseq_build): De-duplicate iseq labels and source locations.
* re.c (rb_reg_initialize): Use rb_fstring() for regex string.
* string.c (rb_fstring): Handle non-string and already-fstr arguments.
* vm_eval.c (eval_string_with_cref): De-duplicate eval source filename.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43866 b2dd03c8-39d4-4d8f-98ff-823fe69b080e