cmd/compile: print block auxint value in HTML output

The auxint value was being printed in LongString() but not LongHTML().

Fixes #38250.

Change-Id: I28e819feef8710f912bee424d1b900eb07f3abb8
Reviewed-on: https://go-review.googlesource.com/c/go/+/227160


Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>