For rootcling do not RegisterModule but parse what we need (SPI-546).
Delay the #include until after the selection.
Split typedefs (needed by name NormContext and thus genreflex) from rest.
Use the proper ROOT include path; only minimal includes for genreflex.
TRootIOCtor is needed by rootcling/genreflex.
Merge: expose less headers to genreflex (SPI-546).
Temporarily #include TObject for genreflex.

Until we have the new class state, determining the TClass property "inherits from TClass" requires TObject.h.
As all STL types have their std stripped, and as EmitStreamerInfo() needs to find the classes, genreflex also needs using std.