Compile BufferHubServer_test for 64-bit on a 64-bit platform

and 32-bit on a 32-bit platform.

Bug: 125885800
Test: m BufferHubServer_test on walleye_xr only generates 64bit target.
Change-Id: Iad9930739bc15e55a7af0d2c357910ffcb098aed
diff --git a/services/bufferhub/tests/Android.bp b/services/bufferhub/tests/Android.bp
index 8d29923..3033e70 100644
--- a/services/bufferhub/tests/Android.bp
+++ b/services/bufferhub/tests/Android.bp
@@ -11,6 +11,7 @@
         "-Wall",
         "-Werror",
     ],
+    compile_multilib: "first",
     header_libs: [
         "libdvr_headers",
         "libnativewindow_headers",