[Sanitizer] Get rid of Symbolizer::Get() and Symbolizer::GetOrNull().

We may as well just use Symbolizer::GetOrInit() in all the cases.
Don't call Symbolizer::Get() early in tools initialization: these days
it doesn't do any important setup work, and we may as well create the
symbolizer the first time it's actually needed.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@217558 91177308-0d34-0410-b5e6-96231b3b80d8