Lua debugger: use sds_malloc() to allocate eval cli array.

Redis-cli handles the debugger "eval" command in a special way since
sdssplitargs() would not be ok: we need to send the Redis debugger the
whole Lua script without any parsing. However in order to later free the
argument vector inside redis-cli using just sdsfreesplitres(), we need
to allocate the array of SDS pointers using the same allocator SDS is
using, that may differ to what Redis is using.

So now a newer version of SDS exports sds_malloc() and other allocator
functions to give access, to the program it is linked to, the allocator
used internally by SDS.

src/sds.h

@@ -258,6 +258,14 @@ sds sdsRemoveFreeSpace(sds s);
 size_t sdsAllocSize(sds s);
 void *sdsAllocPtr(sds s);
 
+/* Export the allocator used by SDS to the program using SDS.
+ * Sometimes the program SDS is linked to, may use a different set of
+ * allocators, but may want to allocate or free things that SDS will
+ * respectively free or allocate. */
+void *sds_malloc(size_t size);
+void *sds_realloc(void *ptr, size_t size);
+void sds_free(void *ptr);
+
 #ifdef REDIS_TEST
 int sdsTest(int argc, char *argv[]);
 #endif