GCC: atoi + printf does not work when linking with ucrt

[Blackhex]

Repro case:

• Build the toolchain with ucrt.
• Compile with aarch64-w64-mingw32-gcc atoi.c

// atoi.c
#include <stdlib.h>
#include <stdio.h>

int main() {
  int test = atoi("20");
  printf("%d\n", test);
}

• Run ./a.out.
• Prints random integer, e.g., -385877008, instead of 20.

Notes:

• Does not happen with msvcrt.
• Does not happen when the binary is compiled with -D__USE_MINGW_ANSI_STDIO=1.
• Both atoi and printf alone seem to work, only this particular composition causes the issue.
• Might be a duplicate of GCC: Impliment Microsoft variadic ABI #10 or GCC: va_list structure is corrupted #70.