Fix bogusly declared WERRORs in kernel build

Many arm kernel configs bogusly specified WERROR=-Werror. There's no
reason for this because the default is that and there's no reason to
override. These date from a time when we needed to add additional
warning->error suppression. They are obsolete and were cut and paste
propagated from file to file.

Comment out all the WERROR=.... lines in powerpc. They aren't bogus,
but were appropriate for the old defaults for gcc4.2.1. Now that we've
made the policy decision to suppress -Werror by default on these
platforms, it is appropriate to comment these out. People wishing to
fix these errors can still un-comment them out, or say WERROR=-Werror
on the command line.

Fix two instances (cut and paste propagation) of hard-coded -Werror
in x86 code. Replace with ${WERROR} instead. This is a no-op change
except for people who build WERROR=-Wno-error :).

This should fix tinderbox / CI breakage.