Build fails with ffi.h

[dsyer]

Same thing happens for me on Binder and in Codepsaces when I run docker build .:

...
#9 24.74     x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -fdebug-prefix-map=/build/python3.5-5Cvh2K/python3.5-3.5.3=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -DUSE__THREAD -DHAVE_SYNC_SYNCHRONIZE -I/usr/include/ffi -I/usr/include/libffi -I/usr/include/python3.5m -c c/_cffi_backend.c -o build/temp.linux-x86_64-3.5/c/_cffi_backend.o
#9 24.74     c/_cffi_backend.c:15:17: fatal error: ffi.h: No such file or directory
#9 24.74      #include <ffi.h>
#9 24.74                      ^
#9 24.74     compilation terminated.
#9 24.74     error: command 'x86_64-linux-gnu-gcc' failed with exit status 1
#9 24.74     
#9 24.74     ----------------------------------------
#9 24.96 Command "/usr/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-zhc6pw0h/cffi/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-pqk0y4sv-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-zhc6pw0h/cffi/
------
executor failed running [/bin/sh -c ([ -f requirements.txt ]     && pip3 install --no-cache-dir -r requirements.txt)         || pip3 install --no-cache-dir jupyter jupyterlab]: exit code: 1