IWYU: Update CMake code for IWYU built with Clang 6

IWYU now correctly requires `<utility>` for `std::move`.  It also
requires a container header when used via a range-based for loop.

Source/cmMakefileExecutableTargetGenerator.cxx

@@ -6,6 +6,7 @@
 #include <memory> // IWYU pragma: keep
 #include <sstream>
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "cmGeneratedFileStream.h"