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>