Unnecessary overhead with stack protector.

[Dave Jones <davej@redhat.com>]

113c5413cf9051cc50b88befdc42e3402bb92115 introduced a change that
made CC_STACKPROTECTOR_ALL not-selectable if someone enables CC_STACKPROTECTOR.

We've noticed in Fedora that this has introduced noticable overhead on
some functions, including those which don't even have any on-stack variables.

According to the gcc manpage, -fstack-protector will protect functions with
as little as 8 bytes of stack usage. So we're introducing a huge amount
of overhead, to close a small amount of vulnerability (the >0 && <8 case).

The overhead as it stands right now means this whole option is unusable for
a distro kernel without reverting the above commit.

	Dave