I checked this now twice: I installed all prequisite packages as written in die Edison Board Support Package User Guide on Page 7.
My operating system is Ubuntu 14.04.1 LTS (trusty).
I deleted the whole build folder and kept the downloads. After that I tried to build the image from scratch. Again, the same error occured. I do not know what might be wrong?
// Edit (with workaround):
Okay it seems that a simple "cmake"-call is missing. E.g. if I download libwebsockets from git:
git clone git://git.libwebsockets.org/libwebsockets
and change into libwebsockets and call cmake like this:
cmake .
The following files are generated:
libwebsockets-test-server.key.pem
libwebsockets-test-server.pem
The same works if I navigate to build/tmp/work/core2-32-poky-linux/libwebsockets/1.23-r0/build and call "cmake ." -> the required files are generated.
So maybe this cmake call is somehow missing in the yocto-configuration? But wait, how can libwebsockets then be compiled? I don't get it. Nevertheless, generating these files by yourself should be a workaround