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/python3/python3.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 PYTHON3_VERSION_MAJOR = 3.9
-PYTHON3_VERSION = $(PYTHON3_VERSION_MAJOR).1
+PYTHON3_VERSION = $(PYTHON3_VERSION_MAJOR).2
 PYTHON3_SOURCE = Python-$(PYTHON3_VERSION).tar.xz
 PYTHON3_SITE = https://python.org/ftp/python/$(PYTHON3_VERSION)
 PYTHON3_LICENSE = Python-2.0, others
@@ -49,6 +49,12 @@ endif
 
 PYTHON3_INSTALL_STAGING = YES
 
+ifeq ($(BR2_PACKAGE_PYTHON3_2TO3),y)
+PYTHON3_CONF_OPTS += --enable-lib2to3
+else
+PYTHON3_CONF_OPTS += --disable-lib2to3
+endif
+
 ifeq ($(BR2_PACKAGE_PYTHON3_READLINE),y)
 PYTHON3_DEPENDENCIES += readline
 else
@@ -156,7 +162,6 @@ PYTHON3_CONF_OPTS += \
 	--with-system-ffi \
 	--disable-pydoc \
 	--disable-test-modules \
-	--disable-lib2to3 \
 	--disable-tk \
 	--disable-nis \
 	--disable-idle3 \