Use arm instruction set with clang 7.0 LTO

* surfaceflinger.so uses LTO.
  clang 7.0 LTO inlined more code and some references
  are too far away to use thumb instructions.

Bug: 72619014
Test: run Forrest
Change-Id: Ia09931e93a170ac58007f80da2d580bb9b9635a6
diff --git a/libs/vr/libbufferhub/Android.bp b/libs/vr/libbufferhub/Android.bp
index 39814cc..e6803da 100644
--- a/libs/vr/libbufferhub/Android.bp
+++ b/libs/vr/libbufferhub/Android.bp
@@ -48,6 +48,11 @@
         "-Wall",
         "-Werror",
     ],
+    arch: {
+        arm: {
+            instruction_set: "arm",
+        },
+    },
     export_include_dirs: localIncludeFiles,
     shared_libs: sharedLibraries,
     header_libs: headerLibraries,