build: add the missing includes only a Windows build reports (#16110)

src/libslic3r/utils.cpp

@@ -119,6 +119,7 @@
 // We are using quite an old TBB 2017 U7, which does not support global control API officially.
 // Before we update our build servers, let's use the old API, which is deprecated in up to date TBB.
 #include <tbb/tbb.h>
+#include <string.h>
 
 namespace boost::posix_time { class ptime; }
 #if ! defined(TBB_VERSION_MAJOR)