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/timescaledb/0018-Update-compat.h.patch

@@ -0,0 +1,27 @@
+From 67744f30f481a05e3cb6a2e73c0cb17117a2eb38 Mon Sep 17 00:00:00 2001
+From: fidomax <adobegitler@gmail.com>
+Date: Mon, 11 Jan 2021 14:16:06 +0300
+Subject: [PATCH] Update compat.h
+
+Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
+Fetch from: https://github.com/timescale/timescaledb/pull/2801/commits/6a927ee84c91797025fc48ac4aab74c3344ebdad.patch
+---
+ src/compat.h | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/src/compat.h b/src/compat.h
+index 1b2ed8e5..6b461e38 100644
+--- a/src/compat.h
++++ b/src/compat.h
+@@ -371,7 +371,7 @@ get_vacuum_options(const VacuumStmt *stmt)
+ #define list_delete_cell_compat(l, lc, prev) list_delete_cell((l), (lc))
+ #define list_make5(x1, x2, x3, x4, x5) lappend(list_make4(x1, x2, x3, x4), x5)
+ #define list_make5_oid(x1, x2, x3, x4, x5) lappend_oid(list_make4_oid(x1, x2, x3, x4), x5)
+-#define for_each_cell_compat(cell, list, initcell) for_each_cell ((cell), (list), (initcell))
++#define for_each_cell_compat(cell, list, initcell) for_each_cell (cell, list, initcell)
+ #endif
+ 
+ /* PG13 removes the natts parameter from map_variable_attnos */
+-- 
+2.29.2
+