[ASan] NFC: make use of a new ErrorBase ctor

Summary:
Minor style changes to complement D44404:
- make use of a new ErrorBase ctor
- de-duplicate a comment about VS2013 support

Reviewers: eugenis

Subscribers: kubamracek, delcypher, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D45390

llvm-svn: 329586