Support building 64-bit windows binaries for Clang.

Bug: http://b/22414702

(cherry picked from commit cbd79ddc82c258f208102177108ced28d1aa1611)

Change-Id: I1836e202000c440225bd68f9c0adb081c216b1c1
diff --git a/build.py b/build.py
index bb7ba36..ebffff1 100755
--- a/build.py
+++ b/build.py
@@ -159,7 +159,11 @@
         'bin/clang' + bin_ext,
         'bin/clang++' + bin_ext,
     ]
-    if host != 'windows-x86':
+    if is_windows:
+        built_files.extend([
+            'bin/clang_32' + bin_ext,
+        ])
+    else:
         built_files.extend([
             'bin/FileCheck' + bin_ext,
             'bin/llvm-as' + bin_ext,