Merge branch 'bugfix/silence-clang-yaspgrid-warnings' into 'master'

[yaspgrid] Silence lots of compiler warnings in clang

See merge request !270

(cherry picked from commit 202e3872)

f4c11fb6 [yaspgrid] Silence lots of compiler warnings in clang
5 jobs for cherry-pick-202e3872 in 51 minutes and 1 second (queued for 25 minutes and 54 seconds)
Status Job ID Name Coverage
  Test
passed #28128
duneci
debian:10 gcc:c++17

00:28:59

passed #28130
duneci
debian:9--clang

00:28:02

passed #28129
duneci
debian:9--gcc

00:26:21

passed #28132
duneci
ubuntu:16.04--clang

00:22:28

passed #28131
duneci
ubuntu:16.04--gcc

00:21:10