Fix stack shuffle such that sj includes si and the last element actually
gets a chance to be reordered.

gcc4: emit warning when ignoring alignment constraints

Currently, GCC 4.2 silently ignores the "aligned" attribute for
objects allocated on the stack if the specified minimum alignment
exceeds the platform's natural stack alignment. This has bitten us in
the past, so we shouldn't allow this to continue.

Fixing the "ignores" problem seems hard, so this commit settles for
tackling the "silently" problem instead.

ok miod, and possibly guenther and deraadt

When the stack protector heuristics doesn't cover a function, leave
a little pointer-sized gap before the return value. This protects
from common off-by-one type of bugs and costs nothing: the attacker
won't be able to overwrite return pointer. Developed at m2k14,
thanks for the hackathon!

Introduce -fstack-shuffle, which randomizes local stack variables.
This will make the environment more hostile and help detect bugs
that depend on overrunning one variable into another, with almost
no performance cost.

Discussed with Theo at m2k14 hackathon. "oh god yes" tedu@, "oh nice" djm@

Add a new option "-fstack-protector-strong" for GCC4. This includes
additional functions to be protected --- those that have local array
definitions, or have references to local frame addresses.

Note 1: Han explicitly licensed this under GPLv2 for us.
Note 2: Do *not* use this anywhere in "src" Makefiles, as the other
GCC doesn't have this option yet (but I'm working on it).

branches: 1.1.1;
Initial revision