Fail to compile for raspberry pi target

[borisdering]

Description: Hello, I'm very to new to Yocto so excuse me if this is a mistake on my behalf but I was not able to build the meta-micropython layer with the raspberrypi target. I receiving the same error that the ffi.h header is missing, this header seams to usually live inside the libffi.

Steps to reproduce:

1. clone the meta-micropython layer into sources
2. add it to your bblayers.conf

# POKY_BBLAYERS_CONF_VERSION is increased each time build/conf/bblayers.conf
# changes incompatibly
POKY_BBLAYERS_CONF_VERSION = "2"

BBPATH = "${TOPDIR}"
BBFILES ?= ""

BBLAYERS ?= " \
  /opt/yocto/workspace/sources/poky/meta \
  /opt/yocto/workspace/sources/poky/meta-poky \
  /opt/yocto/workspace/sources/poky/meta-yocto-bsp \
  /opt/yocto/workspace/sources/meta-raspberrypi \
  /opt/yocto/workspace/sources/meta-micropython \
  /opt/yocto/workspace/sources/meta-example \
  "

3. create an image and add an depends and install it by

# base this image on core image base because we do not want to 
# create a new image, instead use a given one 
require recipes-core/images/core-image-base.bb

DEPENDS += " micropython"

IMAGE_INSTALL += "micropython"

Results:
It seams the micropython is looking for the ffi.h header file and is not able to find it.

....
| modffi.c:32:10: fatal error: ffi.h: No such file or directory
|  #include <ffi.h>
|           ^~~~~~~
| compilation terminated.
| ../py/mkrules.mk:73: recipe for target 'build/genhdr/qstr.i.last' failed
| make: *** [build/genhdr/qstr.i.last] Error 1
| make: *** Deleting file 'build/genhdr/qstr.i.last'
| make: Leaving directory '/opt/yocto/workspace/raspberrypi-build/tmp/work/cortexa7t2hf-neon-vfpv4-poky-linux-gnueabi/micropython/1.8.7-r1.0/git/unix'
| ERROR: oe_runmake failed
| WARNING: /opt/yocto/workspace/raspberrypi-build/tmp/work/cortexa7t2hf-neon-vfpv4-poky-linux-gnueabi/micropython/1.8.7-r1.0/temp/run.do_compile.24621:1 exit 1 from 'exit 1'
| ERROR: Function failed: do_compile (log file is located at /opt/yocto/workspace/raspberrypi-build/tmp/work/cortexa7t2hf-neon-vfpv4-poky-linux-gnueabi/micropython/1.8.7-r1.0/temp/log.do_compile.24621)
ERROR: Task (/opt/yocto/workspace/sources/meta-micropython/recipes-devtools/micropython/micropython_1.8.7.bb:do_compile) failed with exit code '1'
NOTE: Tasks Summary: Attempted 3412 tasks of which 3394 didn't need to be rerun and 1 failed.
...

Expectations:
I did expect that the image build successfully.