mingw: add missing vscprintf.c file

closes #13733

Thanks to @kcbanner for finding this.

lib/libc/mingw/stdio/_vscprintf.c

@@ -0,0 +1,86 @@
+/**
+ * This file has no copyright assigned and is placed in the Public Domain.
+ * This file is part of the mingw-w64 runtime package.
+ * No warranty is given; refer to the file DISCLAIMER.PD within this package.
+ */
+#include <windows.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+/* emulation of _vscprintf() via _vsnprintf() */
+static int __cdecl emu_vscprintf(const char * __restrict__ format, va_list arglist)
+{
+    char *buffer, *new_buffer;
+    size_t size;
+    int ret;
+
+    /* if format is a null pointer, _vscprintf() returns -1 and sets errno to EINVAL */
+    if (!format) {
+        _set_errno(EINVAL);
+        return -1;
+    }
+
+    /* size for _vsnprintf() must be non-zero and buffer must have place for terminating null character */
+    size = strlen(format) * 2 + 1;
+    buffer = malloc(size);
+
+    if (!buffer) {
+        _set_errno(ENOMEM);
+        return -1;
+    }
+
+    /* if the number of characters to write is greater than size, _vsnprintf() returns -1 */
+    while (size < SIZE_MAX/2 && (ret = _vsnprintf(buffer, size, format, arglist)) < 0) {
+        /* in this case try with larger buffer */
+        size *= 2;
+        new_buffer = realloc(buffer, size);
+        if (!new_buffer)
+            break;
+        buffer = new_buffer;
+    }
+
+    free(buffer);
+
+    if (ret < 0) {
+        _set_errno(ENOMEM);
+        return -1;
+    }
+
+    return ret;
+}
+
+#ifndef __LIBMSVCRT_OS__
+
+int (__cdecl *__MINGW_IMP_SYMBOL(_vscprintf))(const char * __restrict__, va_list) = emu_vscprintf;
+
+#else
+
+#include <msvcrt.h>
+
+static int __cdecl init_vscprintf(const char * __restrict__ format, va_list arglist);
+
+int (__cdecl *__MINGW_IMP_SYMBOL(_vscprintf))(const char * __restrict__, va_list) = init_vscprintf;
+
+static int __cdecl init_vscprintf(const char * __restrict__ format, va_list arglist)
+{
+    HMODULE msvcrt = __mingw_get_msvcrt_handle();
+    int (__cdecl *func)(const char * __restrict__, va_list) = NULL;
+
+    if (msvcrt)
+        func = (int (__cdecl *)(const char * __restrict__, va_list))GetProcAddress(msvcrt, "_vscprintf");
+
+    if (!func)
+        func = emu_vscprintf;
+
+    return (__MINGW_IMP_SYMBOL(_vscprintf) = func)(format, arglist);
+}
+
+#endif
+
+int __cdecl _vscprintf(const char * __restrict__ format, va_list arglist)
+{
+    return __MINGW_IMP_SYMBOL(_vscprintf)(format, arglist);
+}

src/mingw.zig

@@ -539,6 +539,7 @@ const msvcrt_common_src = [_][]const u8{
     "stdio" ++ path.sep_str ++ "acrt_iob_func.c",
     "stdio" ++ path.sep_str ++ "snprintf_alias.c",
     "stdio" ++ path.sep_str ++ "vsnprintf_alias.c",
+    "stdio" ++ path.sep_str ++ "_vscprintf.c",
     "misc" ++ path.sep_str ++ "_configthreadlocale.c",
     "misc" ++ path.sep_str ++ "_get_current_locale.c",
     "misc" ++ path.sep_str ++ "invalid_parameter_handler.c",