Issue #12326: sys.platform is now always 'linux2' on Linux

Even if Python is compiled on Linux 3.
diff --git a/configure.in b/configure.in
index c4ad4e8..3e60d8e 100644
--- a/configure.in
+++ b/configure.in
@@ -290,6 +290,7 @@
 	MACHDEP="$ac_md_system$ac_md_release"
 
 	case $MACHDEP in
+	linux*) MACHDEP="linux2";;
 	cygwin*) MACHDEP="cygwin";;
 	darwin*) MACHDEP="darwin";;
         irix646) MACHDEP="irix6";;