Bump Buildroot to 2021.02-rc3 (#1260)

* Rebase patches to Buildroot 2021.02-rc3

* Update Buildroot to 2021.02-rc3

* Declare Kernel headers to be Linux version 5.10 (since they are, and new Buildroot knows about 5.10)

buildroot/package/binutils/2.35.2/0001-sh-conf.patch

@@ -0,0 +1,48 @@
+From ae50e875f4292c99b859cded1d036e401b6ddaec Mon Sep 17 00:00:00 2001
+From: Romain Naour <romain.naour@gmail.com>
+Date: Fri, 25 Dec 2015 11:38:13 +0100
+Subject: [PATCH] sh-conf
+
+Likewise, binutils has no idea about any of these new targets either, so we
+fix that up too.. now we're able to actually build a real toolchain for
+sh2a_nofpu- and other more ineptly named toolchains (and yes, there are more
+inept targets than that one, really. Go look, I promise).
+
+[Romain: rebase on top of 2.32]
+Signed-off-by: Romain Naour <romain.naour@gmail.com>
+[Thomas: rebase on top of 2.29, in which sh64 support was removed.]
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
+---
+ configure    | 2 +-
+ configure.ac | 2 +-
+ 2 files changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/configure b/configure
+index 54d0339ab9e..c2f51ffcebb 100755
+--- a/configure
++++ b/configure
+@@ -3937,7 +3937,7 @@ case "${target}" in
+   nvptx*-*-*)
+     noconfigdirs="$noconfigdirs target-libssp target-libstdc++-v3 target-libobjc"
+     ;;
+-  sh-*-*)
++  sh*-*-*)
+     case "${target}" in
+       sh*-*-elf)
+          ;;
+diff --git a/configure.ac b/configure.ac
+index a910c4fd6ba..a93d93c81c3 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -1178,7 +1178,7 @@ case "${target}" in
+   nvptx*-*-*)
+     noconfigdirs="$noconfigdirs target-libssp target-libstdc++-v3 target-libobjc"
+     ;;
+-  sh-*-*)
++  sh*-*-*)
+     case "${target}" in
+       sh*-*-elf)
+          ;;
+-- 
+2.25.4
+