Reserve space for the future in statvfs(64)

The kernel struct has some spare space at the end too, and some extra
fields, so having a bit of flexibility in statvfs might be worthwhile.

Bug: 14681331
Bug: 12875898
Change-Id: I5b502c5dd9d2e3bb8f34804f83c02669cefce01e
diff --git a/libc/include/sys/statvfs.h b/libc/include/sys/statvfs.h
index 3d8179e..3495546 100644
--- a/libc/include/sys/statvfs.h
+++ b/libc/include/sys/statvfs.h
@@ -23,6 +23,12 @@
 
 __BEGIN_DECLS
 
+#ifdef __LP64__
+#define __STATVFS64_RESERVED uint32_t __f_reserved[6];
+#else
+#define __STATVFS64_RESERVED
+#endif
+
 #define __STATVFS64_BODY \
   unsigned long f_bsize; \
   unsigned long f_frsize; \
@@ -35,10 +41,14 @@
   unsigned long f_fsid; \
   unsigned long f_flag; \
   unsigned long f_namemax; \
+  __STATVFS64_RESERVED
 
 struct statvfs { __STATVFS64_BODY };
 struct statvfs64 { __STATVFS64_BODY };
 
+#undef __STATVFS64_BODY
+#undef __STATVFS64_RESERVED
+
 #define ST_RDONLY      0x0001
 #define ST_NOSUID      0x0002
 #define ST_NODEV       0x0004