[Sanitizer] Introduce ListOfModules object and use it to replace GetListOfModules().

Summary:
This removes the hard limit on the number of loaded modules (used to be
16K), and makes it easier to use LoadedModules w/o causing a memory
leak: ListOfModules owns the modules, and makes sure to properly clean
them in destructor.

Remove filtering functionality that is only needed in one place (LSan).

Reviewers: aizatsky

Subscribers: llvm-commits, kcc

Differential Revision: http://reviews.llvm.org/D17470

llvm-svn: 261554