This avoids having to check both flags in two places, and prevents
people from trying to enable WebAssembly in lite mode (which would
currently build, but you still would not get Wasm support).

The downside is that the default value shown by `gn args --list` now
sais `""` instead of `true`.

R=machenbach@chromium.org, rmcilroy@chromium.org
CC=ecmziegler@chromium.org

Bug: v8:11238
Cq-Include-Trybots: luci.v8.try:v8_linux64_no_wasm_compile_rel
Change-Id: Ib2fe6c32cbdeb89895265bb898abf7284c560cc3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2712783
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72957}