libsanitizer merge from upstream r175042

[Jakub Jelinek]

On Wed, Feb 13, 2013 at 02:27:56PM +0100, Richard Biener wrote:
> ASAN could set an ELF flag on the executable to tell the kernel not
> to use prelinked objects?  That is, similar to how we handle executable
> stacks?

But we don't have such a flag right now, and what should old kernels that
don't support it do with that flag?  Should it be some kind of flag that
causes the programs not to run at all on kernel < 3.9 or whenever the flag
would be handled (can be done with .note.ABI-tag section, plus some flag
somewhere), or something else?  In any case, that would mean changes all
through the toolchain (glibc, linkers, kernel), compared to changing
two files in libsanitizer/asan/ (asan_mapping.h and asan_rtl.cc I believe).

	Jakub