wrappers: Print an understandable error if the total command line ends up too long

This can happen if the input command line is barely under the limit,
but ends up exceeding it due to the extra arguments that the wrapper
adds.

One could hope that _tspawnvp would set errno to a helpful error code,
to identify the issue when printing the error with _tperror(), but in
practice, it doesn't.

wrappers/native-wrapper.h

@@ -94,10 +94,19 @@ static inline int _tspawnvp_escape(int mode, const TCHAR *filename, const TCHAR
     while (argv[num_args])
         num_args++;
     const TCHAR **escaped_argv = malloc((num_args + 1) * sizeof(*escaped_argv));
-    for (int i = 0; argv[i]; i++)
+    int total = 0;
+    for (int i = 0; argv[i]; i++) {
         escaped_argv[i] = escape(argv[i]);
+        total += 1 + _tcslen(escaped_argv[i]);
+    }
     escaped_argv[num_args] = NULL;
-    return _tspawnvp(mode, filename, escaped_argv);
+    int ret = _tspawnvp(mode, filename, escaped_argv);
+    if (ret == -1 && total >= 32767) {
+        int err = errno;
+        fprintf(stderr, "command line too long; %d characters\n", total);
+        errno = err;
+    }
+    return ret;
 }
 #else
 static inline int _tcsicmp(const TCHAR *a, const TCHAR *b) {