Define HAS_FEATURE instead of __has_feature

As discussed in: https://codereview.chromium.org/1837563002/

The approach is what's recommended by clang and is safe because __has_feature
was only defined if the compiler didn't provide it, but nonetheless it's good to
be consistent.

[email protected]

Review URL: https://codereview.chromium.org/1866473002

Cr-Commit-Position: refs/heads/master@{#385541}
2 files changed