waf: cmake: do a clean configuration

We need to remove CMakeCache.txt, otherwise cached variables would remain the
old value when they are removed from cmake_vars parameter.

We use `os.remove()` instead of `Node.delete()` because the latter removes the
node instance from its parent's children list. That makes the node be ignored
when storing persistent information after the build, thus the node signature
wouldn't be saved with that approach, which would make waf always think that
the task should be executed.

Tools/ardupilotwaf/cmake.py

@@ -97,6 +97,7 @@ from waflib import Node, Task, Utils
 from waflib.TaskGen import feature, taskgen_method
 
 from collections import OrderedDict
+import os
 
 class cmake_configure_task(Task.Task):
     vars = ['CMAKE_BLD_DIR']
@@ -120,6 +121,15 @@ class cmake_configure_task(Task.Task):
     def keyword(self):
         return 'CMake Configure'
 
+# Clean cmake configuration
+cmake_configure_task._original_run = cmake_configure_task.run
+def _cmake_configure_task_run(self):
+    cmakecache_path = self.outputs[0].abspath()
+    if os.path.exists(cmakecache_path):
+        os.remove(cmakecache_path)
+    self._original_run()
+cmake_configure_task.run = _cmake_configure_task_run
+
 class cmake_build_task(Task.Task):
     run_str = '${CMAKE} --build ${CMAKE_BLD_DIR} --target ${CMAKE_TARGET}'