Disable v8_use_snapshot by default in 32-bit mac->win cross builds.

The snapshot requires building host code in target bitness, and
chromium's base doesn't build in 32-bit on mac hosts due to some
64-bit-only assembly code.

Bug: chromium:794838
Change-Id: I89887fe63c88c435bc4743c3d99f22ffe79a5bd6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1534635
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60467}

gni/v8.gni

@@ -39,7 +39,10 @@ declare_args() {
   # https://v8.dev/blog/custom-startup-snapshots
   # TODO(thakis): Make snapshots work in 64-bit win/cross builds,
   # https://803591
-  v8_use_snapshot = !(is_win && host_os != "win" && target_cpu == "x64")
+  # On Mac hosts, 32-bit builds targeting Windows can't use snapshots, see
+  # https://crbug.com/794838
+  v8_use_snapshot = !(is_win && host_os != "win" && target_cpu == "x64") &&
+                    !(is_win && host_os == "mac" && target_cpu == "x86")
 
   # Enable several snapshots side-by-side (e.g. default and for trusted code).
   v8_use_multi_snapshots = false