0b8b11d747
This patch makes mingwclang builds compile with -include _mingw.h. This makes MSVC-style constants defined from the start of C++ files rather than at the point where they start including files that depend on _mingw.h. Thus, mingwclang builds will behave more closely to regular builds, potentially avoiding future backouts for mingwclang build failures and/or successful but incorrect mingwclang builds. Differential Revision: https://phabricator.services.mozilla.com/D195662