symbol.c: make dsym_fstrs an identity hash
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49842 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
symbol.c: make dsym_fstrs an identity hash
as the keys are unique fstrings, to get rid of running hash and
compare methods and causing new object allocation during garbage
collection phase. [ruby-dev:48891] [Bug #10933]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49842 b2dd03c8-39d4-4d8f-98ff-823fe69b080e