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/0013-Adjust-copy-code-to-PG13-changes.patch

@@ -0,0 +1,34 @@
+From 5cea3a687f7227997deb0eacbb061c586c6713f7 Mon Sep 17 00:00:00 2001
+From: Sven Klemm <sven@timescale.com>
+Date: Sat, 26 Sep 2020 02:57:38 +0200
+Subject: [PATCH] Adjust copy code to PG13 changes
+
+PG13 adds a CmdType argument to ExecComputeStoredGenerated.
+
+https://github.com/postgres/postgres/commit/c6679e4fca
+
+Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
+Fetch from: https://github.com/timescale/timescaledb/pull/2498/commits/a2d15828cbbbe7570afb03bb930df083ddeafd7a.patch
+---
+ src/copy.c | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/src/copy.c b/src/copy.c
+index c8ce93e6..e38ae15e 100644
+--- a/src/copy.c
++++ b/src/copy.c
+@@ -379,7 +379,11 @@ copyfrom(CopyChunkState *ccstate, List *range_table, Hypertable *ht, void (*call
+ 			/* Compute stored generated columns */
+ 			if (resultRelInfo->ri_RelationDesc->rd_att->constr &&
+ 				resultRelInfo->ri_RelationDesc->rd_att->constr->has_generated_stored)
++#if PG13_GE
++				ExecComputeStoredGenerated(estate, myslot, CMD_INSERT);
++#else
+ 				ExecComputeStoredGenerated(estate, myslot);
++#endif
+ #endif
+ 			/*
+ 			 * If the target is a plain table, check the constraints of
+-- 
+2.29.2
+