spec_helper.rb: libruby.so iff enable-shared

* spec/ruby/optional/capi/spec_helper.rb (compile_extension):
  search libruby.so only when enable-shared.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61495 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/optional/capi/spec_helper.rb

@@ -23,7 +23,7 @@ def compile_extension(name)
   ext = "#{name}_spec"
   lib = "#{object_path}/#{ext}.#{RbConfig::CONFIG['DLEXT']}"
   ruby_header = "#{RbConfig::CONFIG['rubyhdrdir']}/ruby.h"
-  libruby_so = RbConfig::CONFIG['LIBRUBY_SO']
+  libruby_so = RbConfig::CONFIG['LIBRUBY_SO'] if RbConfig::CONFIG["ENABLE_SHARED"] == "yes"
 
   begin
     mtime = File.mtime(lib)