Describe the bug
With cilium/ebpf, it is not possible reference kconfig variables like LINUX_KERNEL_VERSION.

To Reproduce
Steps to reproduce the behavior. Please include:

# Try to bpf2go a file which contains the following line:
# extern int LINUX_KERNEL_VERSION __kconfig;
foo_bpfel.go: can't load BPF from ELF: load BTF: reference to .kconfig: not supported

Expected behavior
We should be able to reference kconfig variables.