CMakePM: Fix build on Windows

Amends 3aa324ef1f.

Change-Id: Ieef98239ec4fa029da1541b15229a17beeb513f6
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cmakeprojectmanager/cmakeconfigitem.cpp

@@ -472,6 +472,11 @@ bool CMakeConfigItem::operator==(const CMakeConfigItem &o) const
     return o.key == key && o.value == value && o.isUnset == isUnset;
 }
 
+uint qHash(const CMakeConfigItem &it)
+{
+    return ::qHash(it.key) ^ ::qHash(it.value) ^ ::qHash(it.isUnset);
+}
+
 #if WITH_TESTS
 
 } // namespace CMakeProjectManager