libsparse: deal with build warning messages

- mostly unused parameters, added defs.h to hold __unused macro
- read_all prototype not included, added output_file.h to acquire

Change-Id: Ib7ee00614acab53a6bd6a64f7e26a8c13dbe6297
diff --git a/libsparse/sparse.c b/libsparse/sparse.c
index 741e8c6..0f107b0 100644
--- a/libsparse/sparse.c
+++ b/libsparse/sparse.c
@@ -19,6 +19,7 @@
 
 #include <sparse/sparse.h>
 
+#include "defs.h"
 #include "sparse_file.h"
 
 #include "output_file.h"
@@ -189,7 +190,7 @@
 	return ret;
 }
 
-static int out_counter_write(void *priv, const void *data, int len)
+static int out_counter_write(void *priv, const void *data __unused, int len)
 {
 	int64_t *count = priv;
 	*count += len;