[NaCl SDK] lua sample: Clean existing naclports installs before building.

native_client_sdk/src/gonacl_appengine/src/lua/build.sh

Index: native_client_sdk/src/gonacl_appengine/src/lua/build.sh
diff --git a/native_client_sdk/src/gonacl_appengine/src/lua/build.sh b/native_client_sdk/src/gonacl_appengine/src/lua/build.sh
index 1a01e5220cf09aec9c3b883a26688f1c0c9a3a80..15a8e02985b42465f8383e18e2fae314689c5672 100755
--- a/native_client_sdk/src/gonacl_appengine/src/lua/build.sh
+++ b/native_client_sdk/src/gonacl_appengine/src/lua/build.sh
@@ -66,8 +66,13 @@ pushd ${NACLPORTS_DIR}
 gclient sync -r ${NACLPORTS_REV}
 popd
 
+
 Banner Building lua
 pushd ${NACLPORTS_DIR}/src
+# Do a 'clean' first, since previous lua build from the naclports bundle
+# building might be installed in the toolchain, and that one is built
+# without readline support.
+make TOOLCHAIN=pnacl clean
 make TOOLCHAIN=pnacl lua-ppapi
 popd