cmMachO: Add missing header for std::unique_ptr

Builds were previously relying on <memory> being included
by <string>, but not all compilers do that and we shouldn't
be relying on that anyway.

Source/cmMachO.h

@@ -5,6 +5,7 @@
 #include "cmConfigure.h" // IWYU pragma: keep
 
 #include <iosfwd>
+#include <memory>
 #include <string>
 
 #if !defined(CMake_USE_MACH_PARSER)