Fixes and cleanup from LTO tree

[Andi Kleen]

Here are a range of bug fixes and cleanups that have accumulated in my
gcc Link Time Optimization (LTO) branches; for issues found
by the compiler when doing global optimization and a few
other issues.

(https://github.com/andikleen/linux-misc lto-*)

IMNSHO they are all useful improvements even without LTO support.

About half of it is in x86 specific code, but the others are
random all over. I tried to always copy the respective maintainers,
but since it's (nearly) a tree sweep I'm also copying Andrew.

-Andi