Make lsan complain loudly when running under ptrace

Summary:
LeakSanitizer does not work with ptrace but currently it
will print warnings (only under verbosity=1) and then proceed
to print tons of false reports.
This patch makes lsan fail hard under ptrace with a verbose message.

https://github.com/google/sanitizers/issues/728

Reviewers: eugenis, vitalybuka, aizatsky

Subscribers: kubabrecka, llvm-commits

Differential Revision: https://reviews.llvm.org/D25538

llvm-svn: 284171