Timestamp: Update workaround to support MinGW alongside MSVC (#296)

Author: Doekin

include/rfl/Timestamp.hpp

@@ -3,9 +3,6 @@
 
 #include <ctime>
 #include <iomanip>
-#include <iostream>
-#include <iterator>
-#include <locale>
 #include <sstream>
 #include <stdexcept>
 #include <string>
@@ -75,8 +72,8 @@ class Timestamp {
   const std::tm& tm() const { return tm_; }
 
  private:
-#ifdef _MSC_VER
-  // This workaround is necessary, because MSVC doesn't support strptime.
+#if defined(_MSC_VER) || defined(__MINGW32__)
+  // This workaround is necessary, because strptime is not available on Windows.
   char* strptime(const char* _s, const char* _f, std::tm* _tm) {
     std::istringstream input(_s);
     input.imbue(std::locale(setlocale(LC_ALL, nullptr)));