[sanitizer] Trivial portion of the port to Myriad RTEMS

This commit contains the trivial portion of the port of ASan to
Myriad RTEMS.
- Whitelist platform in sanitizer_platform.h, ubsan_platform.h
- Turn off general interception
- Use memset for FastPoisonShadow
- Define interception wrappers
- Set errno symbol correctly
- Enable ASAN_LOW_MEMORY
- Enable preinit array
- Disable slow unwinding
- Use fuchsia offline symbolizer
- Disable common code for: InitializeShadowMemory, CreateMainThread,
  AsanThread::ThreadStart, StartReportDeadlySignal,
  MaybeReportNonExecRegion.

Differential Revision: https://reviews.llvm.org/D46454

llvm-svn: 332681