Libsanitizer: merge from master.

Libsanitizer: merge from master.

Merged from revision b638b63b99d66786cb37336292604a2ae3490cfd.

The patch successfully bootstraps on x86_64-linux-gnu and
ppc64le-linux-gnu. I also tested ppc64-linux-gnu that exposed:
https://reviews.llvm.org/D80864 (which is fixed on master).

Abidiff looks happy and I made UBSAN and ASAN bootstrap on
x86_64-linux-gnu.

I'm planning to do merge from master twice a year, once now and
next time short before stage1 closes.

I am going to install the patches as merge from master is obvious
and I haven't made anything special.

libsanitizer/ChangeLog:

	* MERGE: Merge from master.