Implement persistent caching for simplify_condition

Store the results of simplify_condition in a json cache file,
next to the pro2cmake.py script.
Dramatically speeds up re-conversion of projects.

The cache is cleared whenever the content of the
condition_simplifier.py file changes, effectively presuming that the
condition computing code has changed.

Sample times.
Initial corelib.pro conversion - 142.13 seconds.
Next re-conversion with hot cache - 1.17 seconds.

Change-Id: I8790b2736358236e4b23bcb5f10f45a36fdfa426
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Qt CMake Build Bot

0 files changed, 0 insertions, 0 deletions