Ruby

deduplicate strings sooner at load and compile

We can use rb_fstring_cstr in some places to prevent an
intermediate object from being created before deduplication
via rb_fstring.

• compile.c (iseq_compile_each): use rb_fstring_cstr
  (rb_insns_name_array): ditto
• load.c (rb_load_internal0): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57745 b2dd03c8-39d4-4d8f-98ff-823fe69b080e