[liba] Define calloc

To silence a warning in LZ4. The code is not even built.

liba/include/stdlib.h

@@ -9,6 +9,7 @@ LIBA_BEGIN_DECLS
 void free(void *ptr);
 void * malloc(size_t size);
 void * realloc(void *ptr, size_t size);
+void * calloc(size_t count, size_t size);
 
 void abort(void) __attribute__((noreturn));