Implement C23 printf 'w' length modifiers

wN: Specifies that a following b, d, i, o, u, x, or X
conversion specifier applies to an integer argument with
a specific width where N is a positive decimal integer with
no leading zeros

Bug: b/271903607
Test: adb shell
Change-Id: I688f6cefeb2e5c8325b007a59935a46f4116ac29
diff --git a/libc/stdio/printf_common.h b/libc/stdio/printf_common.h
index e761835..b0055f0 100644
--- a/libc/stdio/printf_common.h
+++ b/libc/stdio/printf_common.h
@@ -528,6 +528,17 @@
       case 'b':
         ADDUARG();
         break;
+      case 'w':
+        n = 0;
+        ch = *fmt++;
+        while (is_digit(ch)) {
+          APPEND_DIGIT(n, ch);
+          ch = *fmt++;
+        }
+        if (n == 64) {
+          flags |= LLONGINT;
+        }
+        goto reswitch;
       default: /* "%?" prints ?, unless ? is NUL */
         if (ch == '\0') goto done;
         break;