optional/capi: fix link on mingw
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58728 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
optional/capi: fix link on mingw
LIBRUBYARG is always necessary unless dynamic lookup is allowed.
strip $(DEFFILE) from DLDFLAGS on mingw.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58728 b2dd03c8-39d4-4d8f-98ff-823fe69b080e