[asan] Generate asm instrumentation in MC.

Generate entire ASan asm instrumentation in MC without
relying on runtime helper functions.

Patch by Yuri Gorshenin.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212455 91177308-0d34-0410-b5e6-96231b3b80d8