Relax pthreads check to avoid win32

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/configure b/configure
index abd38dd..fc664fc 100755
--- a/configure
+++ b/configure
@@ -1302,7 +1302,7 @@
   fi
 done
 
-if test "$pthread" = no; then
+if test "$mingw32" != yes -a "$pthread" = no; then
   echo
   echo "Error: pthread check failed"
   echo "Make sure to have the pthread libs and headers installed."