Don't generate code to register record types that have only
been declared, i.e. that have no fields defined in them.
This allows libraries to created which only contain device
support without the record types that they support. The
library must have a DBD file that may declare the record
types (to avoid generating a warning) and also contains any
other device(), variable(), function() and registrar()
entries for software included in the library.
Adds -l flag to the registerRecordDeviceDriver program,
which results in epicsExportSharedSymbols being defined
and shareLib.h being reloaded so the generated output file
can be linked into the library that it is registering.
This aspect has not been tested on Windows DLLs yet.
