[PATCH newlib] libc/include/malloc.h: Add prototype for GNU extension malloc_usable_size()

This is not provided by the newlib malloc implementation but may
be available in external implementations.
---
 newlib/libc/include/malloc.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/newlib/libc/include/malloc.h b/newlib/libc/include/malloc.h
index a9dc5bca6..e73095e1e 100644
--- a/newlib/libc/include/malloc.h
+++ b/newlib/libc/include/malloc.h
@@ -137,6 +137,10 @@ extern void __malloc_lock(struct _reent *);
 
 extern void __malloc_unlock(struct _reent *);
 
+#if __GNU_VISIBLE
+extern size_t malloc_usable_size(void *);
+#endif
+
 /* A compatibility routine for an earlier version of the allocator.  */
 
 extern void mstats (char *);
-- 
2.24.4