fix absl_hash linker error

[sadguitarius]

I'm running an unconventional 64-bit setup on Manjaro Arm. Every now and then something breaks compilation, I guess having something to do with compiler toolchains getting out of sync. Recently I've been unable to compile on the develop branch without linking to absl_hash. Is it ok to merge this, assuming it doesn't break anything with the default toolchain?

[sadguitarius]

ok looks like the check builds are failing so maybe not...

[rdmark]

Right, since the library doesn't exist in the CI build environment we get this error:

/usr/lib/gcc-cross/arm-linux-gnueabihf/11/../../../../arm-linux-gnueabihf/bin/ld: cannot find -labsl_hash: No such file or directory

Have you tried passing this linker flag to the build system by the LDLIBS environment variable?

[sadguitarius]

So LDLIBS doesn't appear to work but LDFLAGS does. Looks like protobuf added an explicit dependency on abseil at some point, so I guess the version used by Ubuntu in the workflow is older than that. Adding the linker flag works for me, so I'll go ahead and close this. It would be easy enough to add the flag for any packaging scripts that needed it as well. Good news is that everything still works with the newer protobuf version!

[rdmark]

aha, that explains it

yes, we're currently stuck at a quite old protobuf / protoc version (v3 release series I believe) because we still target Raspbian Bullseye as the baseline platform, and this is the OS that we build our release images for

there are a multitude of technical reasons for being stuck Raspbian Bullseye, all of which can certainly be overcome with some research and effort; happy to break them down for you if you're interested :)

[sadguitarius]

Oh ok that totally makes sense. It's easy enough to add the flag. I guess if something breaks the protobuf API on distros that use the latest version this could be revisited but it's fine for now.