BC: Move builddirectory handling into BC itself

Use setBuildDirectory() in the different BuildConfigurations instead
of reimplementing that over and over again.

Change-Id: Ic355fdb4624c71667ce470b3e2865c9a8722ef09
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/cmakeprojectmanager/cmakeopenprojectwizard.h

@@ -78,7 +78,7 @@ public:
 
         BuildInfo(CMakeBuildConfiguration *bc)
             : sourceDirectory(bc->target()->project()->projectDirectory())
-            , buildDirectory(bc->buildDirectory())
+            , buildDirectory(bc->buildDirectory().toString())
             , environment(bc->environment())
             , useNinja(bc->useNinja())
             , kit(bc->target()->kit())