using POSIX compatible version of strdup() (i.e. _strdup()) on windows

src/lmpwindows.h

@@ -4,6 +4,7 @@
 #endif
 #include <direct.h>
 #include <cmath>
+#include <cstring>
 // LAMMPS uses usleep with 100 ms arguments, no microsecond precision needed
 #if !defined(__MINGW32__)
 #include "sleep.h"
@@ -15,6 +16,7 @@
 #define ATOBIGINT _atoi64
 
 #define pclose _pclose
+#define strdup _strdup
 
 // the following functions ared defined to get rid of
 // 'ambiguous call to overloaded function' error in VSS for mismathched type arguments