Parallel builds fail (make -j >=2) when using --extra-cflags "--save-temps"

specs:
Host kernel: Linux 4.19.16-1-lts
Host type: x86_64 GNU/Linux
Host distro: Archlinux
Guest: we never get that far
QEMU commit: 9f33051abce238ab43a23125e237aac8b0931b88


steps:
# fresh copy of the latest commit
> git clone https://git.qemu.org/git/qemu.git

# separate build dir
> mkdir build
> cd build

# sample configuration for riscv (this happens for other targets as well)
> ../qemu/configure --target-list=riscv64-softmmu --enable-debug --extra-cflags='-O0 -g3 -save-temps' --prefix=/install/riscv-qemu

# this will fail (see attached log file)
> make -j 2