fix minor compile errors

include/pocketpy/common.h

@@ -2,6 +2,7 @@
 
 #include <cmath>
 #include <cstring>
+#include <ctime>
 
 #include <stdexcept>
 #include <vector>

include/pocketpy/str.h

@@ -153,6 +153,10 @@ struct SStream{
     void write_hex(i64);
 };
 
+#ifdef _S
+#undef _S
+#endif
+
 template<typename... Args>
 Str _S(Args&&... args) {
     SStream ss;