configure.in: insert a space for non-GCC

* configure.in (DLDFLAGS): insert a space between option and its
  argument for non-GCC compilers.  [ruby-core:61429] [Bug #9624]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45348 b2dd03c8-39d4-4d8f-98ff-823fe69b080e