epee: detect strptime, use std::get_time as fallback

CMakeLists.txt

@@ -868,5 +868,9 @@ option(INSTALL_VENDORED_LIBUNBOUND "Install libunbound binary built from source
 
 CHECK_C_COMPILER_FLAG(-std=c11 HAVE_C11)
 
+include(CheckLibraryExists)
+include(CheckFunctionExists)
+
 check_library_exists(c memset_s "string.h" HAVE_MEMSET_S)
 check_library_exists(c explicit_bzero "strings.h" HAVE_EXPLICIT_BZERO)
+check_function_exists(strptime HAVE_STRPTIME)

contrib/epee/include/storages/portable_storage_val_converters.h

@@ -150,8 +150,14 @@ POP_WARNINGS
         else if (boost::regex_match (from, boost::regex("\\d{4}-[01]\\d-[0-3]\\dT[0-2]\\d:[0-5]\\d:[0-5]\\dZ")))
         {
           // Convert to unix timestamp
+#ifdef HAVE_STRPTIME
           struct tm tm;
           if (strptime(from.c_str(), "%Y-%m-%dT%H:%M:%S", &tm))
+#else
+          std::tm tm = {};
+          std::istringstream ss(from);
+          if (ss >> std::get_time(&tm, "%Y-%m-%dT%H:%M:%S"))
+#endif
             to = std::mktime(&tm);
         } else
           ASSERT_AND_THROW_WRONG_CONVERSION();