Set MOZILLA_OFFICIAL on Windows builds

We needed to disable MOZILLA_OFFICIAL on Windows builds as those build were crashing with it. See: legacy/trac#27865 (moved). The underlying problem is using --gc-section in binutils 2.26.1 (See: https://bugzilla.mozilla.org/show_bug.cgi?id=1470772#c8). We should probably either backport the necessary binutils fix or (preferred) bump binutils to something > 2.26.1, which is, alas, currently blocked on https://sourceware.org/bugzilla/show_bug.cgi?id=23466. (See: legacy/trac#26148 (moved))