win ninja/make: Always use a native compiler executable with MSVS 2017

A host-native executable will always be used, and it will be a cross
compiler if the target architecture differs from the host architecture.

BUG=683729

Change-Id: I02a09e1755dd2ab7eca5c9d1957d7aeb56db6af6
Reviewed-on: https://chromium-review.googlesource.com/486400
Commit-Queue: Mark Mentovai <mark@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>

pylib/gyp/MSVSVersion.py

@@ -89,18 +89,27 @@ def _SetupScriptInternal(self, target_arch):
     if self.sdk_based and sdk_dir and os.path.exists(setup_path):
       return [setup_path, '/' + target_arch]
 
+    is_host_arch_x64 = (
+      os.environ.get('PROCESSOR_ARCHITECTURE') == 'AMD64' or
+      os.environ.get('PROCESSOR_ARCHITEW6432') == 'AMD64'
+    )
+
     # For VS2017 (and newer) it's fairly easy
     if self.short_name >= '2017':
       script_path = JoinPath(self.path,
                              'VC', 'Auxiliary', 'Build', 'vcvarsall.bat')
-      return [script_path, target_arch]
+
+      # Always use a native executable, cross-compiling if necessary.
+      host_arch = 'amd64' if is_host_arch_x64 else 'x86'
+      msvc_target_arch = 'amd64' if target_arch == 'x64' else 'x86'
+      arg = host_arch
+      if host_arch != msvc_target_arch:
+        arg += '_' + msvc_target_arch
+
+      return [script_path, arg]
 
     # We try to find the best version of the env setup batch.
     vcvarsall = JoinPath(self.path, 'VC', 'vcvarsall.bat')
-    is_host_arch_x64 = (
-      os.environ.get('PROCESSOR_ARCHITECTURE') == 'AMD64' or
-      os.environ.get('PROCESSOR_ARCHITEW6432') == 'AMD64'
-    )
     if target_arch == 'x86':
       if self.short_name >= '2013' and self.short_name[-1] != 'e' and \
          is_host_arch_x64: