[mksnapshot] Properly handle --target-os=ios

Bug: v8:9103
Change-Id: I7ff6bb0032fd5d81339401bbf8276baf19af8489
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1631417
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61853}

src/snapshot/embedded/platform-embedded-file-writer-base.cc

@@ -119,7 +119,7 @@ EmbeddedTargetOs ToEmbeddedTargetOs(const char* s) {
     return EmbeddedTargetOs::kChromeOS;
   } else if (string == "fuchsia") {
     return EmbeddedTargetOs::kFuchsia;
-  } else if (string == "mac") {
+  } else if (string == "ios" || string == "mac") {
     return EmbeddedTargetOs::kMac;
   } else if (string == "win") {
     return EmbeddedTargetOs::kWin;