www/chromium: Reduce build log spam

[cem]

Summary

Avoid build log spam by disabling a noisy and purely false-positive warning in
targeted locations. The Clang static analysis of pthread locking primitives
assumes they are not wrapped (as well as relatively simple locking use). These
headers simply wrap the underlying primitives and tickle hundreds of false
positives with deep include stacks that spam build logs.

[jrm]

Looks much better. Thanks.