Correction for Packaging rules documentation

[EricC]

I have a found a reference to x86_86 which I think should be x86_64 instead.

All packages compiled for the x86_86 architecture should be compiled with CFLAGS="-O2 -fPIC" and/or CXXFLAGS="-O2 -fPIC", unless a "reasonable" condition exists to do otherwise.

[thenktor]

fixed by gapan