Merge topic 'update-jsoncpp'

ffc6be33a7 IWYU: Map jsoncpp internal header to its public header
d7dfb84f89 Merge branch 'upstream-jsoncpp' into update-jsoncpp
0b97650518 jsoncpp 2020-09-25 (9059f5ca)
d9f8e39357 jsoncpp: Update script to get jsoncpp 1.9.4

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !6514