Ruby

deduplicate static rb_str_format format strings

Anybody who hits these code paths can hit them again in the
future, so try deduplicating across multiple runs of these
methods to reduce garbage.

• string.c (str_upto_each): fstring on "%.*d"
• strftime.c (rb_strftime_with_timespec): fstring on "%0*d"

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57997 b2dd03c8-39d4-4d8f-98ff-823fe69b080e