[clang] [clang] replaced the usage of `asctime` with `strftime` (PR #99075)

[Aaron Ballman via cfe-commits]

================
@@ -1721,11 +1721,13 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
     Diag(Tok.getLocation(), diag::warn_pp_date_time);
     // MSVC, ICC, GCC, VisualAge C++ extension.  The generated string should be
     // of the form "Ddd Mmm dd hh::mm::ss yyyy", which is returned by asctime.
-    const char *Result;
+    const char *Result = "??? ??? ?? ??:??:?? ????";
+    char TimeString[64];
     if (getPreprocessorOpts().SourceDateEpoch) {
       time_t TT = *getPreprocessorOpts().SourceDateEpoch;
       std::tm *TM = std::gmtime(&TT);
-      Result = asctime(TM);
+      if (strftime(TimeString, sizeof TimeString, "%a %b %e %T %Y", TM) != 0)
----------------
AaronBallman wrote:

SHOOT, yes, that is expected, same for `%a`.

> This is why i suggested the C++ approach here https://github.com/llvm/llvm-project/pull/99075#issuecomment-2233382915

We can't use that approach because we need to compile in C++17 mode: https://compiler-explorer.com/z/xosc68WMn

Okay, so how's this for horrible:
```
bool Failed = false;
if (const char *OldLocale = ::setlocale(LC_TIME, "C")) {
  if (strftime(...)) {
  } else {
    Failed = true;
  }
  ::setlocale(LC_TIME, OldLocale);
} else {
  Failed = true;
}

if (Failed) {
  // Emit question marks instead
}
```

https://github.com/llvm/llvm-project/pull/99075