cannot extract release tarball on case-insensitive filesystems

Extracting the release tarball for qemu-2.10.0 results in an error on case-insensitive filesystems because of the files qemu-2.10.0/roms/u-boot/scripts/Kconfig and qemu-2.10.0/roms/u-boot/scripts/kconfig.

All other files are extracted correctly, and the resulting source can be built correctly.

But tar returns with an error, which creates difficulties when trying to automate the build process (e.g: homebrew).