Fix clang compiler settings, and properly set up warnings so they don't interfere with gtest and gmock

Merge from core, and update several missing DLL exports. This does not resolve them all (in particular, node_data::equals seems to be still missing, even though it is inlined in a header, which seems strange).

warning C4800: forcing value to bool 'true' or 'false' (performance warning)

for the node test, since it really doesn't make any sense in this context. (It's exactly what we intended with the "unspecified bool type".)