[Sanitizers] Make abort_on_error common flag.

Summary:
Teach all sanitizers to call abort() instead of _exit() after printing
an error report, if requested. This behavior is the default on Mac OS.

Reviewers: kcc, kubabrecka

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12332

llvm-svn: 246205