Support cross-compiling Windows binaries on Linux

This defines another mutator between HostOrDevice and Arch that will
expand host modules into a module for each host type
(Darwin/Linux/Windows) that is currently being built.

Change-Id: I4c8ac6b616c229f6bd45ad8a35902652fb6a4fff
diff --git a/Android.bp b/Android.bp
index 4d1d701..9a7beb8 100644
--- a/Android.bp
+++ b/Android.bp
@@ -130,6 +130,7 @@
 
         "cc/x86_darwin_host.go",
         "cc/x86_linux_host.go",
+        "cc/x86_windows_host.go",
     ],
     testSrcs: [
         "cc/cc_test.go",