[scudo][standalone] Add missing va_end() in ScopedString::append

[xNombre]

Summary

In ScopedString::append va_list ArgsCopy is created but never cleanuped
which can lead to undefined behaviour, like stack corruption.

[cryptoad]

Thank you, good catch!!

[cryptoad]

Do you need me to commit this?

compiler-rt/lib/scudo/standalone/string_utils.cpp

void ScopedString::append(const char *Format, va_list Args) {
   // formatString doesn't currently support a null buffer or zero buffer length,
   // so in order to get the resulting formatted string length, we use a one-char
   // buffer.
   char C[1];
   const uptr AdditionalLength =
       static_cast<uptr>(formatString(C, sizeof(C), Format, Args)) + 1;
   String.resize(Length + AdditionalLength);
   formatString(String.data() + Length, AdditionalLength, Format, ArgsCopy);
+  va_end(ArgsCopy);
   Length = strlen(String.data());
   CHECK_LT(Length, String.size());
 }
 
 FORMAT(2, 3)
 void ScopedString::append(const char *Format, ...) {
   va_list Args;
   va_start(Args, Format);