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).