Fix missing build_config #include in search_engine_choice.

This header was previously transitively provided by `raw_ptr`. I am
going to remove it, causing this file to fail compiling.

We must include (directly) what we use. This patch fixes it.

Bug: 1508847
Change-Id: Ie4fa2fac7e546715a155e1d63c86198455308ee8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5097572
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Angela Yoeurng <yoangela@chromium.org>
Commit-Queue: Angela Yoeurng <yoangela@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1234581}

diff --git a/components/search_engines/search_engine_choice_utils.h b/components/search_engines/search_engine_choice_utils.h
index 6da123ab..e867cb3e 100644
--- a/components/search_engines/search_engine_choice_utils.h
+++ b/components/search_engines/search_engine_choice_utils.h

@@ -6,6 +6,7 @@
 #define COMPONENTS_SEARCH_ENGINES_SEARCH_ENGINE_CHOICE_UTILS_H_
 
 #include "base/memory/raw_ptr.h"
+#include "build/build_config.h"
 #include "components/search_engines/search_engine_type.h"
 
 namespace policy {