Generate the code (extra runtime calls) for --trace-ignition support at
compile time, based on a #define (similar to TRACE_MAPS). Then check for
--trace-ignition at run-time when deciding whether to actually print
anything. This should make --trace-ignition less painful to use.

Note that --trace-igition is disabled by default, even on debug builds.
It has to be enabled with the gn arg "v8_enable_trace_ignition=true"

As a drive-by, TRACE_MAPS is renamed to V8_TRACE_MAPS, for consistency,
and SFI unique index (needed both by --trace-ignition and --trace-maps)
is cleaned up to be behind another #define.

Change-Id: I8dd0c62d0e6b7ee9c75541d45eb729dc03acbee9
Reviewed-on: https://chromium-review.googlesource.com/506203
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45346}