[ASAN] Sanitize testsuite for ARM.

Address failures exhibited by ARMv8 bot in Thumb mode:

- Fix logic for fast unwinding support (i.e feature is not available for Thumb)
- Fix Unsupported and Requires rules to handle armv8 as well as soft and hard
  float targets
- Un-xfail passing tests

Differential Revision: https://reviews.llvm.org/D47575

llvm-svn: 333729