From: Herton R. Krzesinski on
gitlab.com
https://gitlab.com/cki-project/kernel-ark/-/merge_requests/2749#note_1609...
The way to do it in this case should be:
```TPROGS_CFLAGS="%{?build_hostcflags}" %{make} %{?_smp_mflags} ARCH=$Arch V=1
M=samples/bpf/ VMLINUX_H="${RPM_VMLINUX_H}" || true```
Pass the variable before the make invocation. So make does not override it and
will append. However, that may still Makefile modification if it doesn't use
override or doesn't append with ```+=```.