QtCreator fails to start clangbackend.exe (timeout after 10000ms)

When ClangCodeModel plugin is enabled, all versions except 4.2.1 fail to start the clangbackend.exe executable, therefore not providing any C++ support.

The exact message received during startup is:

Clang Code Model: Error: The clangbackend executable "C:\Qt\Tools\QtCreator\bin\clangbackend.exe" could not be started (timeout after 10000ms).

This affects both x86 and x64 installations of QtCreator.