extmk.rb: non-installed extensions cannot link statically

* ext/extmk.rb: exclude extension libraries not to be installed
  unless shared library is built, as they cannot be linked
  statically.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46035 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/extmk.rb

@@ -519,6 +519,9 @@ cond = proc {|ext, *|
   }.find_all {|ext|
     with_config(ext, &cond)
   }.sort
+  if $LIBRUBYARG_SHARED.empty?
+    exts.delete_if {|d| File.fnmatch?("-*", d)}
+  end
 end
 
 if $extout