The exec bit was missing on prebuild.sh as committed in PR #15
(it landed mode 0644). Running './prebuild.sh' fails with
'Permission denied'; bash ./prebuild.sh works as a workaround but
the shebang is intended to do its job.
Caught while running the first linux-ampere-fourier build on
boltzmann today. README.md examples show './prebuild.sh' so users
will hit the same error.
Single-bit fix via git update-index --chmod=+x. No content change.