make: add __clang_analyzer__ to clang-tidy

We have code that acts slightly differently when the static analyzer is
running, so that it can produce more accurate diagnostics (e.g. less
false positives). It uses __clang_analyzer__ to detect the static
analyzer.

When the static analyzer is run via clang-tidy, __clang_analyzer__
doesn't get defined.

Bug: None
Test: WITH_TIDY=1 m. clang-tidy now acts as expected in code made for
the static analyzer

Change-Id: Ib2a815c0bd67553af465b64207bb480fb52cfaf8