[clang-tidy] Define __clang_analyzer__ macro for clang-tidy for compatibility...

[clang-tidy] Define __clang_analyzer__ macro for clang-tidy for compatibility with clang static analyzer

This macro is widely used in many well-known projects, ex. Chromium.
But it's not set for clang-tidy, so for ex. DCHECK in Chromium is not considered as [[no-return]], and a lot of false-positive warnings about nullptr dereferenced are emitted.
This patch fixes the issue by explicitly added macro definition.

Differential Revision: https://reviews.llvm.org/D44906

llvm-svn: 328932