[openwrt/openwrt] prereq-build: add python 3.9 support

[LEDE Commits]

aparcar pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/e224a9a98fac9e86e7cf77446c2d95777021a72e

commit e224a9a98fac9e86e7cf77446c2d95777021a72e
Author: Rosen Penev <rosenp at gmail.com>
AuthorDate: Thu Oct 29 00:12:16 2020 -0700

    prereq-build: add python 3.9 support
    
    Fixes unmet dependency issue.
    
    Signed-off-by: Rosen Penev <rosenp at gmail.com>
---
 include/prereq-build.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/prereq-build.mk b/include/prereq-build.mk
index 8181812599..e7314b253b 100644
--- a/include/prereq-build.mk
+++ b/include/prereq-build.mk
@@ -149,6 +149,7 @@ $(eval $(call SetupHostCommand,perl,Please install Perl 5.x, \
 $(eval $(call CleanupPython2))
 
 $(eval $(call SetupHostCommand,python,Please install Python >= 3.5, \
+	python3.9 -V 2>&1 | grep 'Python 3', \
 	python3.8 -V 2>&1 | grep 'Python 3', \
 	python3.7 -V 2>&1 | grep 'Python 3', \
 	python3.6 -V 2>&1 | grep 'Python 3', \
@@ -156,6 +157,7 @@ $(eval $(call SetupHostCommand,python,Please install Python >= 3.5, \
 	python3 -V 2>&1 | grep -E 'Python 3\.[5-9]\.?'))
 
 $(eval $(call SetupHostCommand,python3,Please install Python >= 3.5, \
+	python3.9 -V 2>&1 | grep 'Python 3', \
 	python3.8 -V 2>&1 | grep 'Python 3', \
 	python3.7 -V 2>&1 | grep 'Python 3', \
 	python3.6 -V 2>&1 | grep 'Python 3', \