Clang: preamble*.pch temporary files are not deleted

Qt Creator when using the clang code model creates under %temp% on Windows files like preamble-47dd7e.pch which correspond with a C++ header or source file.

Unfortunately these files are not deleted when a document is closed or when Qt Creator is closed.

These files vary in size but together can eat-up Gigabytes of disk space. I've noticed this because Windows complained of low disk space.