Merge r368219 (PR42988)

    Restrict the NetBSD ASan TSD fallback to !ASAN_DYNAMIC
    
    The fallback to the alternative implementation of TSD with TLS
    is only needed for the static version of ASan for NetBSD.
    
    The same code cannot be reused for the dynamic version of ASan as
    TLS breaks and TSD code works.

llvm-svn: 369341