D28596 added SANITIZER_INTERFACE_WEAK_DEF which can guarantee `*_default_options` are always defined.
The weak attributes on the `__{asan,lsan,msan,ubsan}_default_options` declarations can thus be removed.
`MaybeCall*DefaultOptions` no longer need nullptr checks, so their call sites can just be replaced by `__*_default_options`.
Reviewed By: #sanitizers, vitalybuka
Differential Revision: https://reviews.llvm.org/D87175