ProjectExplorer: Trigger environment evaluation on current project change

This makes e.g. %{CurrentProject:VcsTopLevelPath} in the kit's
environment much more useful.

Task-number: QTCREATORBUG-20752
Change-Id: I4bf49e61a7a7281a6c9bf039a1d9118b6e4060ef
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -79,6 +79,9 @@ BuildConfiguration::BuildConfiguration(Target *target, Core::Id id)
             this, &BuildConfiguration::updateCacheAndEmitEnvironmentChanged);
     connect(this, &BuildConfiguration::environmentChanged,
             this, &BuildConfiguration::emitBuildDirectoryChanged);
+    // Many macroexpanders are based on the current project, so they may change the environment:
+    connect(ProjectTree::instance(), &ProjectTree::currentProjectChanged,
+            this, &BuildConfiguration::updateCacheAndEmitEnvironmentChanged);
 }
 
 Utils::FileName BuildConfiguration::buildDirectory() const