[UBSan] Use shared library for UBSan on OS X (compiler-rt part).

Summary:
Switch to shared library for UBSan. Add support for building
UBSan on OSX and iossim by cargo-culting ASan build rules.

Test Plan: regression test suite

Reviewers: zaks.anna, kubabrecka

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8473

llvm-svn: 233036