qtconcurrent/generaterun: adapt to run(QThreadPool *pool,...)

The output is still very different from the checked-in file in QtCore.

Change-Id: I02f7489867b891c7867deebd33a39547c16923e4
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
qtconcurrent/generaterun: adapt to earlier changes in qtconcurrentrun.h

Except for the license header and the new auto return functions, the
qtconcurrentrun.h header is now reproduced faithfully again.

Change-Id: Ib3b1ec10e75ddfb8e4bd8f7d765ce9d2fc1fc4f9
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>