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/0006-Adjust-copy-code-to-PG13-addRTEtoQuery-changes.patch

@@ -0,0 +1,37 @@
+From 196943ff91a6a21c575fbca1f047544970ec4c98 Mon Sep 17 00:00:00 2001
+From: Sven Klemm <sven@timescale.com>
+Date: Thu, 24 Sep 2020 16:18:43 +0200
+Subject: [PATCH] Adjust copy code to PG13 addRTEtoQuery changes
+
+PG13 removes addRTEtoQuery and provides a similar function
+addNSItemToQuery which has a different signature.
+
+https://github.com/postgres/postgres/commit/5815696bc6
+
+Signed-off-by: Maxim Kochetkov <fido_max@inbox.ru>
+Fetch from: https://github.com/timescale/timescaledb/commit/10d1c2d698c1b7cbf5af86082287adda4f0c6e97.patch
+---
+ src/copy.c | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/src/copy.c b/src/copy.c
+index 2e63dc76..c8ce93e6 100644
+--- a/src/copy.c
++++ b/src/copy.c
+@@ -535,7 +535,12 @@ copy_constraints_and_check(ParseState *pstate, Relation rel, List *attnums)
+ {
+ 	ListCell *cur;
+ 	char *xactReadOnly;
+-#if PG12_GE
++#if PG13_GE
++	ParseNamespaceItem *nsitem =
++		addRangeTableEntryForRelation(pstate, rel, RowExclusiveLock, NULL, false, false);
++	RangeTblEntry *rte = nsitem->p_rte;
++	addNSItemToQuery(pstate, nsitem, true, true, true);
++#elif PG12
+ 	RangeTblEntry *rte =
+ 		addRangeTableEntryForRelation(pstate, rel, RowExclusiveLock, NULL, false, false);
+ 	addRTEtoQuery(pstate, rte, false, true, true);
+-- 
+2.29.2
+