[scudo][standalone] Fix Android logging

Summary:
Zygote & children's stderr is lost, so use Bionic's provided allocation
free syslog function for `outputRaw`. Get rid of the mutex as it's not
vital and could cause issues with `fork`.

Reviewers: cferris, pcc, eugenis, hctim, morehouse

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D73561