[pool] Accept custom allocators

lib/common/pool.h

@@ -16,6 +16,7 @@ extern "C" {
 
 
 #include <stddef.h>   /* size_t */
+#include "zstd_internal.h"   /* ZSTD_customMem */
 
 typedef struct POOL_ctx_s POOL_ctx;
 
@@ -27,6 +28,8 @@ typedef struct POOL_ctx_s POOL_ctx;
 */
 POOL_ctx *POOL_create(size_t numThreads, size_t queueSize);
 
+POOL_ctx *POOL_create_advanced(size_t numThreads, size_t queueSize, ZSTD_customMem customMem);
+
 /*! POOL_free() :
     Free a thread pool returned by POOL_create().
 */