Only pass android_toolchain in android builds.

dl/BUILD.gn

Index: dl/BUILD.gn
diff --git a/dl/BUILD.gn b/dl/BUILD.gn
index 3b2f7b758a61cd7bc00a1be7568e91a3262c4ce5..5459f48c109f22a944927888c184811b643919f8 100644
--- a/dl/BUILD.gn
+++ b/dl/BUILD.gn
@@ -27,12 +27,13 @@ config("dl_config") {
 
   if (current_cpu == "arm" && is_clang) {
     # TODO(hans) Enable integrated-as (crbug.com/124610).
-    rebased_android_toolchain_root =
-        rebase_path(android_toolchain_root, root_build_dir)
-    asmflags = [
-      "-fno-integrated-as",
-      "-B${rebased_android_toolchain_root}/bin",  # Else /usr/bin/as gets picked up.
-    ]
+    asmflags = [ "-fno-integrated-as" ]
+    if (is_android) {
+      rebased_android_toolchain_root =
+          rebase_path(android_toolchain_root, root_build_dir)
+      # Else /usr/bin/as gets picked up.
+      asmflags += [ "-B${rebased_android_toolchain_root}/bin" ]
+    }
   }
 }