ProjectExplorer: Add a BuildConfiguration::regenerateBuildFiles

That's effectively a generic hook for "re-run qmake" without the
qmake/QmakeProjectManager dependency.

Change-Id: I236d40690cde9047831422b2651ed2284b220959
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/buildconfiguration.h

@@ -36,6 +36,7 @@ namespace ProjectExplorer {
 class BuildInfo;
 class NamedWidget;
 class BuildStepList;
+class Node;
 class Kit;
 class Target;
 class IOutputParser;
@@ -79,6 +80,8 @@ public:
     virtual bool isEnabled() const;
     virtual QString disabledReason() const;
 
+    virtual bool regenerateBuildFiles(Node *node);
+
     enum BuildType {
         Unknown,
         Debug,