[scudo][standalone] Support __BIONIC__

Summary:
Some Android builds that we are interested in define `__BIONIC__`
but not `__ANDROID__`, so expand `SCUDO_ANDROID` to encompass those.

Reviewers: cferris, hctim, pcc, eugenis, morehouse

Subscribers: krytarowski, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D71772