Fix static shell build failing on Ubuntu 24.04 with a missing firmware ELF

[merkelmarrow]

Building the static shell from source fails on Ubuntu 24.04. Synthesis runs for a while and then stops with a confusing error saying a .elf file "does not exist". The same build works on Ubuntu 22.04, which made the failure look like an unsupported OS rather than a real bug. This change makes the build work on 24.04.

It matches the behaviour reported in #117.

Problem

To work around an issue running Vivado inside containers, SLASH preloads a system library (libudev) into Vivado. That preload is inherited by every process Vivado starts, including the compiler it uses to build the memory controller's calibration firmware. That firmware is what becomes the missing .elf.

On Ubuntu 24.04 that system library started depending on a second library (libcap) that the bundled firmware compiler cannot see. So the compiler fails to start, the firmware is never built, and the error stays hidden until much later, when synthesis looks for the file that was never produced. On Ubuntu 22.04 the library had no such dependency, which is exactly why 22.04 was unaffected.

Investigation

I was able to narrow down the issue with several rounds of A/B tests with a small reproducer of the failing step. The first clue was that the failure could not be reproduced in isolation. Building the design directly with Vivado on the same 24.04 host always succeeded. The only thing that ever failed was the build driven through SLASH's installer, which meant the difference had to be in the environment the installer sets up.

Comparing the installer's Vivado invocation against a direct one, the only meaningful difference was the inherited libudev preload.

no preload -> succeeds
LD_PRELOAD=libudev.so.1 -> fails: "libcap.so.2: cannot open shared object file"
LD_PRELOAD=libudev.so.1:libcap.so.2 -> succeeds

The third line is the fix.

Changes

When SLASH applies the preload, it now also brings along the dependency the preloaded library needs, so the firmware compiles successfully on 24.04.

• No change in behaviour on Ubuntu 22.04 or inside containers.
• The fallback for hosts without the preloaded library is unchanged.

Testing

• Reproduced the failure on a Ubuntu 24.04 host with Vivado 2025.1, using the actual build flow with only the preload differing between the two runs. The firmware ELF is missing before the fix and present after it.
• Added unit tests covering the 24.04 case, the 22.04 case, and the case where the library is absent to catch potential future regressions.
• Full static shell rebuild (starting this now).