Move transformer change tracking out of the build graph loader

The checks that determine whether to re-run prepare scripts and/or
commands due to property or environment changes do not belong into the
build graph loader. Instead, we now do them on demand during the build
process. Advantages:
- The code is at its "natural" place, making it easier to understand
  and less fragile.
- There are a lot fewer unnecessary build data invalidations, speeding
  up both re-resolving and rebuilding in case only some rules/commands
  have changed.
- Re-running commands due to property or environment changes no longer
  implies re-running prepare scripts.
- We now catch property changes on generated artifacts, which was not
  possible before, because the build graph loader only had access to
  the source artifacts of the re-resolved project.

Change-Id: I36b022cf631fa9e8293feec4d6f416c2686539c1
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/lib/corelib/buildgraph/processcommandexecutor.h b/src/lib/corelib/buildgraph/processcommandexecutor.h
index 877c0bffb..1e4b18777 100644
--- a/src/lib/corelib/buildgraph/processcommandexecutor.h
+++ b/src/lib/corelib/buildgraph/processcommandexecutor.h
@@ -80,7 +80,7 @@ private:
 
     void sendProcessOutput();
     void removeResponseFile();
-    const ProcessCommand *processCommand() const;
+    ProcessCommand *processCommand() const;
 
 private:
     QString m_program;