FTBFS: contrib: rav1e

Note that this also occurs for native x86 builds:

cd rav1e && export TARGET_CC=riscv64-linux-gnu-gcc && export TARGET_AR=riscv64-linux-gnu-ar && export TARGET_CFLAGS=" -I/home/remi/videolan/vlc/contrib/riscv64-linux-gnu/include -g -O2" && export RUSTFLAGS="-C panic=abort -C opt-level=z" && . /home/remi/videolan/vlc/contrib/bin/.cargo/env && RUSTUP_HOME=/home/remi/videolan/vlc/contrib/bin/.rustup CARGO_HOME=/home/remi/videolan/vlc/contrib/bin/.cargo cargo capi install --target=riscv64gc-unknown-linux-gnu --prefix=/home/remi/videolan/vlc/contrib/riscv64-linux-gnu --library-type staticlib --release --locked --no-default-features --features=asm
Error: CliError { error: Some(failed to acquire jobserver token

Caused by:
    Bad file descriptor (os error 9)), exit_code: 101 }
make: *** [../src/rav1e/rules.mak:32 : .rav1e] Erreur 1

It works fine with make -j1. The build rules ostensibly do not work properly with the make job server.