This change adds the GOWASM option "signext" to enable the generation of experimental sign-extension operators. The feature is in phase 4 of the WebAssembly proposal process: https://github.com/WebAssembly/meetings/blob/master/process/phases.md More information on the feature can be found at: https://github.com/WebAssembly/sign-extension-ops/blob/master/proposals/sign-extension-ops/Overview.md Change-Id: I6b30069390a8699fbecd9fb4d1d61e13c59b0333 Reviewed-on: https://go-review.googlesource.com/c/go/+/168882 Reviewed-by: Cherry Zhang <cherryyz@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Cherry Zhang <cherryyz@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org>
