Qmake: Add variable chooser to build directory path chooser

Task-number: QTCREATORBUG-17160
Change-Id: I11974b04f1ab7f757fddb7a62bff787a977838ba
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/qmakeprojectmanager/qmakeprojectconfigwidget.cpp

@@ -31,6 +31,7 @@
 #include "ui_qmakeprojectconfigwidget.h"
 
 #include <coreplugin/coreicons.h>
+#include <coreplugin/variablechooser.h>
 #include <projectexplorer/target.h>
 #include <qtsupport/qtkitinformation.h>
 
@@ -82,6 +83,9 @@ QmakeProjectConfigWidget::QmakeProjectConfigWidget(QmakeBuildConfiguration *bc)
     m_ui->inSourceBuildDirEdit->setReadOnly(true);
     m_ui->inSourceBuildDirEdit->setEnabled(false);
 
+    auto chooser = new Core::VariableChooser(this);
+    chooser->addSupportedWidget(m_ui->shadowBuildDirEdit->lineEdit());
+
     m_ui->shadowBuildCheckBox->setChecked(isShadowBuild);
 
     connect(m_ui->shadowBuildCheckBox, &QAbstractButton::clicked,