Use same button type (QToolButton) for all build step buttons.

Makes it look a bit less bad on Mac

src/plugins/projectexplorer/buildstepspage.cpp

@@ -163,7 +163,7 @@ void BuildStepsPage::addBuildStepWidget(int pos, BuildStep *step)
     s.upButton->setIconSize(QSize(10, 10));
     s.downButton->setIconSize(QSize(10, 10));
 #endif
-    s.removeButton = new QPushButton(this);
+    s.removeButton = new QToolButton(this);
     s.removeButton->setText(QChar('X'));
     s.removeButton->setMaximumHeight(22);
     s.removeButton->setMaximumWidth(22);

src/plugins/projectexplorer/buildstepspage.h

@@ -58,7 +58,7 @@ struct BuildStepsWidgetStruct
     Utils::DetailsWidget *detailsWidget;
     QToolButton *upButton;
     QToolButton *downButton;
-    QPushButton *removeButton;
+    QToolButton *removeButton;
 };
 
 class BuildStepsPage : public BuildConfigWidget