libubox: backport upstream commit

Backport: b8abed749423 utils.h: add fallthrough macro
Fixes: #381

package/libs/libubox/Makefile

@@ -1,7 +1,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=libubox
-PKG_RELEASE=1
+PKG_RELEASE=2
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(PROJECT_GIT)/project/libubox.git

package/libs/libubox/patches/001-add-fallthrough-macro.patch

@@ -0,0 +1,37 @@
+From b8abed7494238c22522b29814c4cc754e3c19d5a Mon Sep 17 00:00:00 2001
+From: Felix Fietkau <nbd@nbd.name>
+Date: Sun, 16 May 2021 17:31:57 +0200
+Subject: [PATCH] utils.h: add fallthrough macro
+
+This can be used to silence clang warnings about unannotated fall-through
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+ utils.h | 12 ++++++++++++
+ 1 file changed, 12 insertions(+)
+
+diff --git a/utils.h b/utils.h
+index 5c53cc0..dacac6e 100644
+--- a/utils.h
++++ b/utils.h
+@@ -226,6 +226,18 @@ int clock_gettime(int type, struct timespec *tv);
+ #define __hidden __attribute__((visibility("hidden")))
+ #endif
+ 
++#ifndef __has_attribute
++# define __has_attribute(x) 0
++#endif
++
++#ifndef fallthrough
++# if __has_attribute(__fallthrough__)
++#  define fallthrough __attribute__((__fallthrough__))
++# else
++#  define fallthrough do {} while (0)  /* fallthrough */
++# endif
++#endif
++
+ int b64_encode(const void *src, size_t src_len,
+ 	       void *dest, size_t dest_len);
+ 
+-- 
+2.20.1