decoding support for legacy v0.2 format

lib/zstd.h

@@ -30,7 +30,8 @@
     - zstd source repository : https://github.com/Cyan4973/zstd
     - ztsd public forum : https://groups.google.com/forum/#!forum/lz4c
 */
-#pragma once
+#ifndef ZSTD_H
+#define ZSTD_H
 
 #if defined (__cplusplus)
 extern "C" {
@@ -105,3 +106,5 @@ size_t ZSTD_compressCCtx(ZSTD_CCtx* ctx, void* dst, size_t maxDstSize, const voi
 #if defined (__cplusplus)
 }
 #endif
+
+#endif  /* ZSTD_H */