Cannot build on macOS due to eventfd

[nworb-cire]

eventfd is only available on Linux, so building openpilot and its tools (specifically I'm trying to run cabana) fails on macOS due to the way IPC synchronization was implemented in https://github.com/commaai/cereal/pull/439.

Here is the full error I see, after freshly cloning master and running scons a second time:

$ scons -j8 -u -k
scons: Entering directory `/Users/ebrown1/PycharmProjects/openpilot3'
scons: Reading SConscript files ...
Git commit hash for gitversion.h: e1805f65
scons: done reading SConscript files.
scons: Building targets ...
clang++ -o cereal/messaging/event.os -c -std=c++1z -DGL_SILENCE_DEPRECATION -DSWAGLOG="\"common/swaglog.h\"" -g -fPIC -O2 -Wunused -Werror -Wshadow -Wno-unknown-warning-option -Wno-deprecated-register -Wno-register -Wno-inconsistent-missing-override -Wno-c99-designator -Wno-reorder-init-list -Wno-error=unused-but-set-variable -DGL_SILENCE_DEPRECATION -DSWAGLOG="\"common/swaglog.h\"" -fPIC -I/opt/homebrew/include -I/opt/homebrew/opt/openssl@3.0/include -I. -Ithird_party/acados/include -Ithird_party/acados/include/blasfeo/include -Ithird_party/acados/include/hpipm/include -Ithird_party/catch2/include -Ithird_party/libyuv/include -Ithird_party/json11 -Ithird_party/curl/include -Ithird_party/linux/include -Ithird_party/snpe/include -Ithird_party/mapbox-gl-native-qt/include -Ithird_party/qrcode -Ithird_party -Icereal -Iopendbc/can -Ithird_party/json11 cereal/messaging/event.cc
generate_dbc_json(["tools/cabana/generate_dbc_json"], [])
tools/cabana/dbc/generate_dbc_json.py --out tools/cabana/dbc/car_fingerprint_to_dbc.json
Traceback (most recent call last):
  File "tools/cabana/dbc/generate_dbc_json.py", line 5, in <module>
    from selfdrive.car.car_helpers import get_interface_attr
  File "/Users/ebrown1/PycharmProjects/openpilot3/selfdrive/car/car_helpers.py", line 5, in <module>
    from common.params import Params
  File "/Users/ebrown1/PycharmProjects/openpilot3/common/params.py", line 1, in <module>
    from common.params_pyx import Params, ParamKeyType, UnknownKeyName, put_nonblocking, put_bool_nonblocking # pylint: disable=no-name-in-module, import-error
ModuleNotFoundError: No module named 'common.params_pyx'
scons: *** Error 1
cereal/messaging/event.cc:9:10: fatal error: 'sys/eventfd.h' file not found
#include <sys/eventfd.h>
         ^~~~~~~~~~~~~~~
1 error generated.
scons: *** [cereal/messaging/event.os] Error 1
scons: done building targets (errors occurred during build).

As a temporary workaround, I was able to build cabana by checking out d0a8b3780c in the openpilot repo.

[incognitojam]

https://github.com/commaai/cereal/pull/452 will resolve this

[fredyshox]

Fixed by #476