bug#62954: Valgrind blocks R on powerpc64le

[Andreas Enge]

Currently r-minimal depends on texlive-latex-xkeyval, which depends on
texlive-ms, which for a reason I do not see pulls in the valgrind variable.

This is at version 3.17, which fails on powerpc64le. The user facing
variable valgrind/interactive, however, is at 3.20, and it builds.

After the impending core-updates merge, we should update valgrind to
3.20.

I am opening a bug so that this is not forgotten.

Andreas