sanitizer_common: avoid compiler-interted memset in deadlock detector

Compilers tends to insert memset/memcpy for some struct/array operations,
and these don't play well inside of sanitizer runtimes.
Avoiding these calls was the intention behind internal_memset.
Remove the leftover ={} that can result in memset call.

Reviewed By: vitalybuka, pgousseau

Differential Revision: https://reviews.llvm.org/D106978