### Fix registration of DRVETs

The C++ code generated in an IOC's `RecordDeviceDriver.cpp` file can fail
to compile if the Makefile building the IOC defines the `USE_TYPED_DRVET`
macro. Compiler errors caused by this bug will look something like this:

```
test_registerRecordDeviceDriver.cpp:198:15: error:
typedef 'drvet' cannot be referenced with the 'struct' specifier
  198 | static struct drvet *drvsl[] = {
      |               ^
/epics/base-7.0/include/drvSup.h:38:21: note: declared here
   38 | typedef typed_drvet drvet;
      |                     ^
1 error generated.
```

[This PR](https://github.com/epics-base/epics-base/pull/902)
modifies the generated C++ code to resolve that problem, and adds a
driver to the example IOC template to catch regressions.