See bug report here.

http://mail.openjdk.java.net/pipermail/panama-dev/2018-December/003405.html

I did some more digging, and the culprit seems to be here:

public abstract int sysinfo(java.foreign.memory.Pointer<jextract.dump.usr_include_linux_sysinfo$sysinfo>);

That is, we are generating a symbol in the sysinfo header that refers to some non existing symbol (sysinfo$sysinfo).

So, there are two issues here: first, given the current state, jextract should fail (generating a classfile with dangling reference is no good), secondly, it would be nice if jextract followed the #include directives, which it usually do, but not this time.