...in file qbsproject.cpp, line 940.

The assert can be triggered with e.g.:
 1. Load a bigger qbs project, e.g. qtcreator.qbs.
 2. Trigger project build as soon as possible.
 3. Cancel the "Parsing C/C++" operation.
 4. Wait until the build finished and the assert occurs.

This happens because CppModelManager::updateProjectInfo() since

  commit  536ccc8a
  CppTools: Fix incompletely indexed project

will check whether the previous indexer run was canceled or not. If it
was canceled, it will trigger a full-reindexing of the project.

Updating the compiler call data is a special case and it should never
trigger an indexing operation, so introduce a dedicated update function
for this case.

Change-Id: I456945ccf2bf697aaeada572ed87f3acb21a5eaf
Reviewed-by: Christian Kandeler <christian.kandeler@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>