math.c: fix tgamma
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54492 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
math.c: fix tgamma
[ruby-core:74817] [Bug #12249]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54492 b2dd03c8-39d4-4d8f-98ff-823fe69b080e