CV8: produce LF_MFUNCTION_V2 entry for member functions

So far, member functions of classes and structs are described in the CV8 debug info as normal functions. This causes the VS debugger not to show members of the class/struct without prepending "this->" when stepping through that function.

This patch tunnels the class type pointer through the unused func_t::Fclass member to cv8.c, where appropriate debug type info is generated.