Fix compile error with std.Io.Writer on eZ80

Author: myclevorname

lib/std/os/windows.zig

@@ -4775,7 +4775,10 @@ pub const PEB = extern struct {
         switch (@sizeOf(usize)) {
             4 => 0x22,
             8 => 0x3C,
-            else => unreachable,
+            else => if (builtin.target.os.tag == .windows)
+                @compileError("@sizeOf(usize) is neither 4 nor 8")
+            else
+                0, // avoid compile erros with std.Io.Writer on exotic targets
         }
     ]ULONG,