Similar to the recent change to --code-comments, make --debug-code a
build-time enabled flag, enabled by default on debug builds.

This also removes the emit_debug_code() option from the assembler,
instead using the flag directly (there were no cases where this option
didn't match the global flag).

Change-Id: Ic26b0d37b615a055508c9dda099ffbe979eae030
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843348
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74095}