[asan] Fix a deadlock halt_on_error-signals.c when `reporting_thread_tid_` is 0

A signal can be delivered after TryLock but before StartReporting in ScopedInErrorReport, causing a deadlock.  Fixing this by statically initializing reporting_thread_tid_ to kInvalidTid.

Differential Revision: http://reviews.llvm.org/D20524

llvm-svn: 271256