Build rabbitmq-server and erlang with FIPS enabled from source

I'm trying to install rabbitmq-server on Ubuntu 20.04 with FIPS enabled, and I saw that erlang DEB default packages doesn't have it compiled in them. I read this guide - https://www.erlang.org/doc/apps/crypto/fips.html and built erlang from source with the --enable-fips flag, and it was successfully built and installed, with all the libs in /usr/local/lib/erlang/lib.

Now I tried to also build rabbitmq-server from source (Since the DEB package depends on the erlang packages which I don't want to install) and it seems like it fails to find a certain erlang package - eunit/include/eunit.hrl:

$ make
make[1]: Entering directory '/home/ubuntu/rabbitmq-server/deps/rabbit_common'
make[1]: Leaving directory '/home/ubuntu/rabbitmq-server/deps/rabbit_common'
make[1]: Entering directory '/home/ubuntu/rabbitmq-server/deps/rabbit'
make[2]: Entering directory '/home/ubuntu/rabbitmq-server/deps/rabbit/apps/rabbitmq_prelaunch'
make[2]: Leaving directory '/home/ubuntu/rabbitmq-server/deps/rabbit/apps/rabbitmq_prelaunch'
make[2]: Entering directory '/home/ubuntu/rabbitmq-server/deps/rabbitmq_cli'
 GEN    escript/rabbitmqctl
Resolving Hex dependencies...
Resolution completed in 0.028s
Unchanged:
  amqp 2.1.2
  csv 2.4.1
  dialyxir 0.5.1
  json 1.4.1
  observer_cli 1.7.4
  parallel_stream 1.0.6
  recon 2.5.3
  stdout_formatter 0.2.4
  temp 0.4.7
  x509 0.8.7
==> stdout_formatter
Compiling 4 files (.erl)
stdout_formatter_table.erl:12:14: can't find include lib "eunit/include/eunit.hrl"
could not compile dependency :stdout_formatter, "mix compile" failed. Errors may have been logged above. You can recompile this dependency with "mix deps.compile stdout_formatter --force", update it with "mix deps.update stdout_formatter" or clean it with "mix deps.clean stdout_formatter"
make[2]: *** [Makefile:95: escript/rabbitmqctl] Error 1
make[2]: Leaving directory '/home/ubuntu/rabbitmq-server/deps/rabbitmq_cli'
make[1]: *** [../../erlang.mk:4512: deps] Error 2
make[1]: Leaving directory '/home/ubuntu/rabbitmq-server/deps/rabbit'
make: *** [erlang.mk:4512: deps] Error 2

I tried to add a different erlang library load just before eunit - kernel/include/file.hrl and it successfully loaded that one.

Also tried strace to see where it look, all I found is that it loads either the ERL_LIBS or the DIST_ERL_LIBS variables, tried to set both of them, but the same error.

Any ideas?

After a day of debugging, I found out it was because I was using elixir 15 and didn't use the latest rabbitmq-server, I was using 3.11.9 which is not compatible with it..

I have to use 3.11.9 for production reasons, so I downgraded elixir to 14 and it worked.