Fix build break when building with enable_openvr=true on Windows

third_party/openvr/BUILD.gn

Index: third_party/openvr/BUILD.gn
diff --git a/third_party/openvr/BUILD.gn b/third_party/openvr/BUILD.gn
index 6df649937fe93481746ecf7e4b60fe776c13ee4a..97887cf01d1dfa84ae7bfeb0fdb30b01a72ec3d1 100644
--- a/third_party/openvr/BUILD.gn
+++ b/third_party/openvr/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-loadable_module("openvr") {
+component("openvr") {
   output_name = "openvr_api"
 
   # Some ascii versions of Windows APIs are used in this code.
@@ -24,6 +24,10 @@ loadable_module("openvr") {
     "src/src/vrcommon/vrpathregistry_public.cpp",
   ]
 
+  if (target_cpu == "x64" && is_win) {
+    defines += [ "WIN64" ]
+  }
+
   include_dirs = [
     "src/headers",
     "src/src",