[ASan] Introduce AllocatorOptions to configure allocator behavior.
Summary:
Reduce the dependency of allocator code on runtime flags. Instead,
pass a bunch of options that configure allocator behavior at
initialization or re-initialization. That would allow us to
cleaner modify allocator behavior during a program execution
when ASan is activated or de-activated.
Test Plan: regression test suite
Reviewers: kcc
Subscribers: llvm-commits, eugenis
Differential Revision: http://reviews.llvm.org/D6711
llvm-svn: 224605