BuildConfiguration: Add helper to create a build directory

Use the helper in CMake. Everything else does not seem to directly
create directories.

Change-Id: I50fba8c461471a1bcd0f9c187a857730c35e4f8f
Reviewed-by: hjk <hjk@qt.io>

src/plugins/projectexplorer/buildconfiguration.cpp

@@ -251,6 +251,14 @@ MacroExpander *BuildConfiguration::macroExpander() const
     return &d->m_macroExpander;
 }
 
+bool BuildConfiguration::createBuildDirectory()
+{
+    QDir dir;
+    const auto result = dir.mkpath(buildDirectory().toString());
+    buildDirectoryAspect()->validateInput();
+    return result;
+}
+
 void BuildConfiguration::setInitializer(const std::function<void(const BuildInfo &)> &initializer)
 {
     d->m_initializer = initializer;