Replace usage of std::ctime, which is not safe for use in multithreaded contexts

- std::ctime returns a pointer to a string that "may be shared between
  std::asctime and std::ctime, and may be overwritten on each invocation
  of any of those functions.".
  - https://en.cppreference.com/w/cpp/chrono/c/ctime
- Replaced with call to strftime to generate the same string
  representation (using the format string: %c)
- Leveraged localtime_r (which is thread-safe) to convert time_t to
  struct tm, as required by strftime.

src/utils/string.h

@@ -21,6 +21,11 @@
 #include <utility>
 #include <sstream>
 #include <iomanip>
+#include <time.h>
+
+#ifdef WIN32
+#include "src/compat/msvc.h"
+#endif
 
 #ifndef SRC_UTILS_STRING_H_
 #define SRC_UTILS_STRING_H_
@@ -60,9 +65,11 @@ const char HEX2DEC[256] = {
 
 
 inline std::string ascTime(const time_t *t) {
-    std::string ts = std::ctime(t);
-    ts.pop_back();
-    return ts;
+    struct tm timeinfo;
+    localtime_r(t, &timeinfo);
+    char tstr[std::size("Www Mmm dd hh:mm:ss yyyy")];
+    strftime(tstr, std::size(tstr), "%c", &timeinfo);
+    return tstr;
 }