[Bug sanitizer/59061] Port leaksanitizer

[earthdok at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59061

--- Comment #31 from Sergey Matveev <earthdok at google dot com> ---
(In reply to Kostya Serebryany from comment #30)
> lsan's allocator clears all memory using internal_memset, which is damn
> slow. (sets on byte at a time)
> 
> asan's allocator doesn't do that (it sets first 4K bytes of allocated region
> with garbage using the REAL fast memset)
> 
> I think the right solution is to finally implement *fast* internal_memset. 
> We'll do that. 
> 
> Sergey, can this difference between asan and lsan allocators cause 
> false negatives/positives in lsan?

It can cause a false negative if there's a stale pointer outside of those 4k.
But in practice 4k ought to be enough for anybody.

I think standalone LSan should support the max_alloc_fill_size flag. I'll also
change it to use real memset.