gn2bp: Add protoc to builtin_deps

aprotoc in external/protobuf can be used

Test: ./update_result.sh
Change-Id: I590ecde420bea38f08c9b2f42242b4dd805e995f
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index b616db1..3811c3a 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -221,6 +221,8 @@
         enable_uapi_headers,
     '//src/profiling/memory:bionic_libc_platform_headers_on_android':
         enable_bionic_libc_platform_headers_on_android,
+    '//third_party/protobuf:protoc':
+      lambda x: None,
 }
 
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