2.10.0: Build downloads libffi instead of using the pre-installed version

[yurivict]

Describe the bug

-- Using src='https://github.com/libffi/libffi/archive/master.zip'
CMake Error at libffi-stamp/download-libffi.cmake:170 (message):
  Each download failed!

Package builders aren't allowed to download files during build, so that there is no internet access.

Why doesn't it use the pre-installed libffi?

Build log.

To Reproduce
Regular build.

Expected behavior
Use pre-installed libffi.so

Desktop (please complete the following information):

• OS/Platform: FreeBSD 14.0
• clang-18

Additional context
Add any other context about the problem here.

Following up
Was the issue fixed? Please report back.

[eisenhauer]

Note: A patch has been applied to Dill that may sort this. If we can verify that it works there, we'll pull it in here. (The goal is not to use libffi in the ADIOS build at all.)

[yurivict]

dill builds fine on FreeBSD after the latest PRs.