Explictly pass -marm when arm mode is required

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index cde27848fd6c4515552afe887282ab78dd021bd2..b93c14521939ff04670ebd46db970cc3fabd63d4 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -785,6 +785,14 @@ config("compiler_arm_thumb") {
   }
 }
 
+config("compiler_arm") {
+  if (current_cpu == "arm" && is_chromeos) {
+    # arm is normally the default mode for clang, but on chromeos a wrapper
+    # is used to pass -mthumb, and therefor change the default.
+    cflags = [ "-marm" ]
+  }
+}
+
 # runtime_library -------------------------------------------------------------
 #
 # Sets the runtime library and associated options.