This adds gflags to the list of ignored directories for clang static
analysis and adds "explicit" where required in mutex.h.
We also stop building a duplicate copy of snprintf for windows as our builds
already include a definition for it.
MozReview-Commit-ID: 4uMhTMvAKL0
--HG--
extra : rebase_source : d63d3797053c7720c725b3994cb3b2ca11bb191f