Using a custom font fails with `Unknown message: 0x38` about scenic HOT 12 CLOSED

Erlang/OTP 21 [erts-10.0.2] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1] [hipe]

==> scenic_sensor
Compiling 1 file (.ex)
Generated scenic_sensor app
==> scenic
Compiling 78 files (.ex)
Generated scenic app
==> scenic_driver_glfw
mkdir -p priv/prod
cc -O3 -std=c99 `pkg-config --static --cflags glfw3 glew` -fPIC -o priv/prod/scenic_driver_glfw c_src/main.c c_src/comms.c c_src/nanovg/nanovg.c c_src/utils.c c_src/render_script.c c_src/tx.c `pkg-config --static --libs glfw3 glew` -lGL -lm -lrt
c_src/render_script.c:102:36: error: ‘M_PI’ undeclared here (not in a function); did you mean ‘NVG_PI’?
   static const float        TAU  = M_PI * 2;
                                    ^~~~
                                    NVG_PI
make: *** [Makefile:43: priv/prod/scenic_driver_glfw] Error 1
could not compile dependency :scenic_driver_glfw, "mix compile" failed. You can recompile this dependency with "mix deps.compile scenic_driver_glfw", update it with "mix deps.update scenic_driver_glfw" or clean it with "mix deps.clean scenic_driver_glfw"
==> scenic_2048
** (Mix) Could not compile with "make" (exit status: 2).
You need to have gcc and make installed. If you are using
Ubuntu or any other Debian-based system, install the packages
"build-essential". Also install "erlang-dev" package if not
included in your Erlang/OTP version. If you're on Fedora, run
"dnf group install 'Development Tools'".