In certain situations (especially if the profiler is disabled) it can
happen that multiple isolates trigger tier-up at the same time. Each
recompilation would then identify the set of functions to recompile and
add compilation units for them. This creates lots of redundant
compilation, which takes time and can exceed the total wasm code space
limit (code would later get garbage-collected, but there is a high
peak).
This CL fixes that by always finishing a running recompilation before
starting a new one. Since typically concurrent recompilations all
recompile for the same tier, this would avoid do most compilation only
once, and later recompilations can skip most functions.

The only redundant compilation that can happen is via compilation units
that are still executing while the next recompilation starts, but those
should not create too much redundant code.

R=thibaudm@chromium.org

Bug: chromium:1114093
Change-Id: If8fa7d953f3ce77a9d146458bf5e17bb9bf97219
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2379851
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69588}