Show libffi version only if set

ext/fiddle/extconf.rb

@@ -116,9 +116,9 @@ if ver
   ver = ver.gsub(/-rc\d+/, '') # If ver contains rc version, just ignored.
   ver = (ver.split('.').map(&:to_i) + [0,0])[0,3]
   $defs.push(%{-DRUBY_LIBFFI_MODVERSION=#{ '%d%03d%03d' % ver }})
+  warn "libffi_version: #{ver.join('.')}"
 end
 
-warn "libffi_version: #{ver}"
 case
 when $mswin, $mingw, (ver && (ver <=> [3, 2]) >= 0)
   $defs << "-DUSE_FFI_CLOSURE_ALLOC=1"