First, `"str"` is a string constant but `("str")` is not.  It is a
random expression whose type happen to be const char*.  Second,
non-constant initializer element is forbidden in C90.  Mixture of
these two results in the fact that `{("str")}` is a C99ism.

Just delete the parens and everything goes well.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61553 b2dd03c8-39d4-4d8f-98ff-823fe69b080e