Fixed detection of endianness introduced in fcb5e172abaf.

Previously, NJS_HAVE_LITTLE_ENDIAN was declared unconditionally.

This correctly fixes #326 issue on Github.
diff --git a/auto/endianness b/auto/endianness
index ea83598..953eefa 100644
--- a/auto/endianness
+++ b/auto/endianness
@@ -3,7 +3,6 @@
 # Copyright (C) NGINX, Inc.
 
 njs_found=no
-NJS_BYTE_ORDER=little
 
 njs_feature="system byte ordering"
 njs_feature_name=NJS_BYTE_ORDER
@@ -27,7 +26,7 @@
     exit 1;
 fi
 
-if [ $NJS_BYTE_ORDER = big ]; then
+if [ $njs_feature_value = big ]; then
     njs_define=NJS_HAVE_BIG_ENDIAN . auto/define
 
 else