RELOC_HIDE got miscompiled on gcc3.1/x86-64 in the access to softirq.c's per
cpu variables.  This fixes the problem.

Clearly to hide the relocation the addition needs to be done after the
value obfuscation, not before.

I don't know if it triggers on other architectures (x86-64 is especially
stressf here because it has negative kernel addresses), but seems like the
right thing to do.