Cross build alternate_version_generator.exe for Windows ARM64

Bug: 893460
Change-Id: I5618e7da43eb99e59839549c9669deeb61ee65f6
Reviewed-on: https://chromium-review.googlesource.com/c/1474438Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Tom Tan <Tom.Tan@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#632662}

chrome/installer/test/BUILD.gn

@@ -2,11 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/symlink.gni")
 import("//testing/test.gni")
-
 assert(is_win)
 
-executable("alternate_version_generator") {
+if (current_toolchain == host_toolchain) {
+  executable("alternate_version_generator") {
     testonly = true
     sources = [
       "alternate_version_generator_main.cc",
@@ -21,6 +22,13 @@ executable("alternate_version_generator") {
       "//chrome/installer/util:with_rc_strings",
       "//testing/gtest",
     ]
+  }
+} else {
+  binary_symlink("alternate_version_generator") {
+    testonly = true
+    binary_label = ":$target_name($host_toolchain)"
+    binary_output_name = "alternate_version_generator.exe"
+  }
 }
 
 static_library("alternate_version_generator_lib") {