lcov: unable to find gcov

Hello,

It seems that lcov is unable to find the gcov binary by default. Using a nix-shell as nix-shell -p gcc is a workaround and lcov will find gcov correctly.

Moreover, find /nix/store -name '*gcov*' returns an entry in gcc-7.0.5 ; but currently the default compiler is gcc 10.3.0, I don't know if this is linked to the issue.