[Bug c++/87519] -Wsign-conversion -Wconversion explicit cast fails to silence warning

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87519

--- Comment #12 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed on trunk, will backport to 9.3 later.