playground: update NaCl to trunk.544461
playground: update NaCl to trunk.544461

This pulls in https://crrev.com/c/962675, which fixes the
underlying issue of NaCl mishandling signals during a SIGSEGV.

Fixes golang/go#23836

Change-Id: I562909354ee0e2aec819b9f7116f86f673ccadff
Reviewed-on: https://go-review.googlesource.com/101735
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/playground,golang/playground,golang/playground