win32.c: use _mkgmtime() instead of mktime() in stat()

Conversion to local time seems unnecessary and it apparently causes
issues with DST.

Fixes #20018, #20061

Author: xenu

pod/perldelta.pod

@@ -330,9 +330,18 @@ L</Modules and Pragmata> section.
 
 =over 4
 
-=item XXX-some-platform
+=item Windows
 
-XXX
+=over 4
+
+=item *
+
+In some cases, timestamps returned by L<stat()|perlfunc/stat> and
+L<lstat()|perlfunc/lstat> failed to take daylight saving time into account.
+[L<GH #20018|https://github.com/Perl/perl5/issues/20018>]
+[L<GH #20061|https://github.com/Perl/perl5/issues/20061>]
+
+=back
 
 =back
 

win32/win32.c

@@ -1469,24 +1469,21 @@ win32_kill(int pid, int sig)
 PERL_STATIC_INLINE
 time_t
 translate_ft_to_time_t(FILETIME ft) {
-    SYSTEMTIME st, local_st;
+    SYSTEMTIME st;
     struct tm pt;
 
-    if (!FileTimeToSystemTime(&ft, &st) ||
-        !SystemTimeToTzSpecificLocalTime(NULL, &st, &local_st)) {
+    if (!FileTimeToSystemTime(&ft, &st))
         return -1;
-    }
 
     Zero(&pt, 1, struct tm);
-    pt.tm_year = local_st.wYear - 1900;
-    pt.tm_mon = local_st.wMonth - 1;
-    pt.tm_mday = local_st.wDay;
-    pt.tm_hour = local_st.wHour;
-    pt.tm_min = local_st.wMinute;
-    pt.tm_sec = local_st.wSecond;
-    pt.tm_isdst = -1;
-
-    return mktime(&pt);
+    pt.tm_year = st.wYear - 1900;
+    pt.tm_mon = st.wMonth - 1;
+    pt.tm_mday = st.wDay;
+    pt.tm_hour = st.wHour;
+    pt.tm_min = st.wMinute;
+    pt.tm_sec = st.wSecond;
+
+    return _mkgmtime(&pt);
 }
 
 typedef DWORD (__stdcall *pGetFinalPathNameByHandleA_t)(HANDLE, LPSTR, DWORD, DWORD);