bug fix: libs -> $libs

Author: santana

ext/extconf.rb

@@ -1,6 +1,6 @@
 require 'mkmf'
 
-env = libs = nil
+env = nil
 informixdir = ENV["INFORMIXDIR"]
 MSWindows = /djgpp|(cyg|ms|bcc)win|mingw/
 
@@ -17,17 +17,17 @@
 dir_config("informix", idefault, ldefault)
 
 if RUBY_PLATFORM =~ MSWindows
-  libs += File.join(informixdir, 'lib', 'isqlt09a.lib')
+  $libs += File.join(informixdir, 'lib', 'isqlt09a.lib')
 else
   env = "/usr/bin/env"
 
   %w(ifsql ifasf ifgen ifos ifgls).each do |lib|
-    libs += " " + format(LIBARG, lib)
+    $libs += " " + format(LIBARG, lib)
   end
   $LIBPATH.each do |path|
     checkapi = File.join(path, 'checkapi.o')
     if File.exist?(checkapi)
-      libs += " " + checkapi
+      $libs += " " + checkapi
       break
     end
   end