[Sanitizer] Reduce the usage of sanitizer blacklist in CodeGenModule

Get rid of cached CodeGenModule::SanOpts, which was used to turn off
sanitizer codegen options if current LLVM Module is blacklisted, and use
plain LangOpts.Sanitize instead.

1) Some codegen decisions (turning TBAA or writable strings on/off)
   shouldn't depend on the contents of blacklist.

2) llvm.asan.globals should *always* be created, even if the module
   is blacklisted - soon Clang's CodeGen where we read sanitizer
   blacklist files, so we should properly report which globals are
   blacklisted to the backend.